There she will sit on one of those gilt chairs that are so teeny and uncomfortable for people with bottoms, but positively ample for Nan, who hardly possesses one, and there she will shop.
She won't make any notes on her programme. Nan Kempner, seasoned customer, knows what she wants when she sees it and she remembers it exactly, pocket for pocket, gilt braid for gilt braid. A couple of days later she will order it, to be made exactly to fit her skinny-chic body.
Nan Kempner is the couture customer. She has earned her prized ringside seat in the gilded salon of the Hotel Intercontinental in Paris not by being a movie star, like Catherine Deneuve, who will sit to her right; nor by being a doyenne of the press, like Suzy Menkes, who will sit to her left; but by spending. And spend she does.
Haute couture prices really are a secret. But it is safe to say that a frock costs far more than a family-sized car. Nan buys frocks, she buys jackets, she buys trousers. She wears ball gowns, but rumour has it she does not need to buy them. One of the perks of being a high-profile big spender is that one gets those big entrance dresses on loan - a blessing, as each might cost more than the price of a family-sized house.
Nan (not short for anything, she 'has always just been Nan') has only missed one Yves Saint Laurent haute couture show out of 63. That was last season, when her 88- year-old father, Speed Schlensinger of San Francisco, one-time mandarin of the Ford Motor Corporation, died on the very eve of the Paris season. Nan had to change reservations for New York to Paris to the New York/San Francisco shuttle, where she joined her 'baby stepmother', Gail - more than two decades her junior.
Nan was missed in Paris, where her habitual entrance, sending out air kisses across the salon with one bejewelled and liver-spotted hand, mouthing 'How are you?' to dear friends in the crowd, is always recorded by the paparazzi. She didn't miss anything 5groundbreaking at Saint Laurent, although had she been there she might have invested in an abbreviated suit edged with Chantilly lace. Nan always finds something to like.
She's been there at the best of them - sobbing with joy along with Diana Vreeland at Saint Laurent's Ballets Russes collection (1976, and judged the finest of his career), wiping away tears with Paloma at Yves's Hommage a Picasso collection (1988 and another high point). But even at shows where Yves doesn't sparkle Nan can be relied upon to spot the winners among the morass of reissues and rehashes, and to throw her head back in ecstasy, mouthing 'That's won-der-ful, won-der-ful.'
Nan has known Yves since he was young and skinny. They met when her mother, Irma Schlensinger, took her daughter to Paris and to Dior in 1958. There, Nan, who claims she had only been slightly embarrassed to turn up at school wearing white gloves and carrying a hand-painted lunchbox each day, fell in love - with a white, sleeveless sheath dress and matching white overcoat with ermine cuffs, which cost far more than her clothes allowance.
So she cried. And she cried and she cried, until a gawky boy in glasses, the assistant to Mr Dior, emerged to see what the fuss was about. Nan kept on wailing until the vendeuse reduced the price to within her not inconsiderable means. The pattern of a lifetime was set.
Saint Laurent is stocky now, but Nan is still slim, 'the same size as I was when I married' - to Thomas Lenox Kempner, a banker, and now chairman of Loeb Partners in New York. Nan's exaggerated slimness (she was once wickedly described as 'a skull on a stick') has benefits. 'Yes, it is useful,' explains Nan, 'because I get to buy the mannequins' dresses (those worn once by the models at the show) at discount.'
It is also useful because Yves has always designed best for a skinny, tall body, the female body shape that most resembles his own as it was once, in a prime that had him posing gaunt, lanky and naked for his own perfume advertisements.
'I think about those sample sixes when I'm working out in my gym,' Nan tells me. And work out she does, in a gym in her Park Avenue duplex, where the only room not brimming with antiques is fitted out with matt-black fitness equipment and a trampoline.
Nan Kempner is the original 'social X-ray', the phrase coined by Tom Wolfe to describe the rich and skinny women socialites of Manhattan. Indeed, when the ill-fated movie of The Bonfire of the Vanities was being made, Kim Cattrall (who played the glossy Park Avenue wife) prepared for her role by working out with the original - who exhausted the younger actress with the sheer number of sit-ups in her daily routine.
Nan skis, Nan swims, and when she was younger Nan was renowned for waterskiing from Southampton, New York State, to Fire Island for cocktails, then water-skiing back again - about a 30-mile round trip.
But most of all, Nan loves to shop. And after a catwalk show, this woman who has dedicated her life to clothes knows precisely what to order - particularly from her personal YSL vendeuse. She knows which items to order made-to-measure; what to select from the catwalk samples worn by models 50 years her junior, and what will go with what from the estimated 250 other Yves Saint Laurent couture pieces she has bought at the house since it opened in 1962.
'And that is not counting ready-to-wear. She has thousands of Saint Laurents,' says Joy Hendericks, who, until her departure from the company this month was YSL's extremely social ambassador in New York.
'What do I have from Saint Laurent?' muses Nan. 'The other day I remembered this red and white stripy tweedy jacket I'd boxed away years back and I dug that out again. That's Saint Laurent from his Dior days. Then from his first YSL show, I bought suits mostly, which were divine. I remember exactly what I was wearing to the party for Opium (the YSL fragrance, launched from a Chinese junk moored in the Hudson in 1977), a Le Smoking pant suit, a sheer camisole and a Saint Laurent bra. So I was wearing underwear as outerwear, which is still so modern.
'What else? I have turned all the children's rooms and the nursery into dressing rooms with rails all round which are curtained off into closets, and then there are all my boxes. The other night we went to the most marvellous party and I wore an evening kaftan I'd dug out again, in apricot crepe de Chine embellished with shells and string and tied with a rope belt that was from Yves from the 1960s. Oh, and the 1970s] In the Seventies I was a Moroccan, a Chinese woman, Carmen - I travelled the world through my Saint Laurent clothes. And I was a Russian peasant from the Ballets Russes - I had the brown taffeta skirt with the turquoise blouse, the burgundy cummerbund and the royal blue bolero embroidered in black and trimmed with black braid. I still wear the skirt.
'I remember in the Seventies, our car would drop the kids off at school, then Tommy (Mr Kempner) would pick me up, and he'd say: 'Now, who are we today?' and I'd be Pocahontas, Nanook of the North, I'd be - God knows - the River Boat Queen. It was such fun. And I'd be thrilled and so would Tommy, because he never knew who was going to be in the car with him . . .'
She is, she happily admits, an addict. 'I suppose it's probably better for you than alcohol,' she says. 'I like to think that I have been extravagant - but thriftily so.' But her addiction has never restricted her to one designer alone. Not for her this newfangled 'one-stop shopping'. Yes, Nan loves Yves and Yves loves Nan. But Emanuel Ungaro loves her too, and so does Bill Blass, so does Calvin Klein, so do Karl Lagerfeld and Christian Lacroix ('who is sometimes a little extreme for me, although I adore my dinner-suit with jewelled sleeves that looks like I've been dipped in caviare').
'She wears clothes better than anyone else I know. I am proud she is one of my customers,' says Oscar de la Renta. 'She is The Chic,' says Valentino, who never usually sanctions anything involving designs other than his own. 'She is one of the few women who know how to mix old and new, different designers, and make it superb.'
'Allure, elegance, vivacite, fidele a elle-meme,' Ungaro responds to my request for a comment by return of fax, and so does Calvin Klein: 'Nan is a woman of great style and tremendous energy. She is glamorous and elegant]'
She doesn't stop short at designer labels, either. When I ask Nan about the pressures of 'buying American' she retorts: 'I buy plenty of American; there is, unfortunately, nothing I don't buy.' She then rattles off purchases from the Gap, Banana Republic and the J Crew Catalogue.
But what does she do, now she is in her mid-sixties, with all these clothes? She replies: 'I'm old-fashioned enough to believe a woman should change her clothes for the evening, even when she is at home with her husband.' I want to ask her how many times she changes for each evening in. But as often as Nan is upstairs changing to stay in, she's changing for an evening out.
If she embodies the 'X-ray' of Wolfe's phrase, she certainly embodies the 'social', too. She flew to Paris for the 30th birthday of the House of Saint Laurent. She flew back for 25 years of Ungaro, to Rome for 30 years of Valentino; she always tries to pop over to the late 'Swifty' Lazar's Oscars party in Hollywood. In New York, she throws parties, she throws dinners, she goes to parties, she goes to dinners, she even goes to shop openings. In the past she was wilder, dancing at Regine's ('Oh my God, I was a disco queen, I can remember having my picture taken in my hot pants - I think they were Christian Dior'), at Castels, at Studio 54. One night at Le Jardin, a forerunner of Studio 54, Nan drove photographers wild by jitterbugging with Maxime de la Falaise, mother of Loulou, Saint Laurent's muse, and grandmother of Saint Laurent's super-waif house model, Lucie.
But perhaps her finest hour was in a red sequined sheath dress by Halston. When the late designer won the 1972 Coty Award - American fashion's equivalent of the Oscars - Nan was summoned to appear on stage at Lincoln Center, which she did, in the sequins, standing housewifely at an electric cooker frying eggs-over-easy with bacon.
This mother of three and grandmother of six has said, memorably, that she wants to be buried naked, 'because there are bound to be stores where I'm going'. What she leaves behind will join the clothes she has already given to the Metropolitan Museum of Art in New York, 'or be sold at Christie's, wouldn't that be marvellous?'
Some have been sold already. Skinny, not-so-rich Manhattanites stake out the New York thrift shop to which Nan donates and they also queue for her cast-offs at the annual Lighthouse for the Blind POSH sale, where, it has been rumoured, Nan queues up in disguise to buy stuff back that she can't really bear to part with. 'I hate to give because I know it is just what I'll want to be wearing again next,' she says.
Nan Kempner may be one of the few survivors of that old Manhattan breed, the 'ladies who lunch'. But, unlike most of the lettuce munchers, Nan eats as she shops - with gusto. When we met for lunch once in New York, she had two bloody Marys and eggs Benedict with crumbled bacon on top. She then talked me through the dessert menu with the enthusiasm of a connoisseur: 'Chocolate ice-cream, blood-orange sorbet or the creme brulee . . ?' And then, when she realised I was chanting a private mantra of 'Shall I, shan't I?' said firmly: 'Let's share a creme brulee.' She finished off with a cappuccino, and for post-prandial exercise we went window-shopping at the Gap. Fortune has dealt Nan a good hand. She revels in her own serendipity, claiming that the very worst day of her life was when she slipped and broke her ankle just before her Coming Out so that she couldn't wear her new frock, 'which came from Jean Desses, which was where Valentino worked at that point, and that is how we met. I met Karl Lagerfeld when he was Mr Karl at Patou I think, and I met Chanel when she re-opened her salon (in 1954). I bought a tweed laced ribbon suit in pale blue and brown with a brown mousseline shirt. I met Courreges and Ungaro when they were at Balenciaga. I never shopped there, but my mother did, and of course I shopped from them when they went out alone. I bought high boots and little minis and a jumpsuit with cut-out flowers round the midriff.'
Is there anything she won't wear? 'Oh, a good designer will always make something that is right for me,' she says. 'There's no such thing as a thoroughly bad collection. I love all my clothes. Like Linus and his comfort blanket, I couldn't go out of the house if I didn't like the way I looked. No way could I go around in a running suit or leave the house without putting on at least some lipstick.'
'I run, I don't walk to my plastic surgeon,' she once told the US trade magazine, Women's Wear Daily. 'I'm 65,' she says now. 'Do I look it?' Some would say yes. Others, including her plastic surgeon, would say no. In any case, she is convinced that she will have at least as many years as her father.
All this is rather good news for the supposedly moribund Parisian haute couture. Every season, someone, somewhere, goes to Paris for the first time, enters the hallowed halls and is horrified by the opulence, the excess, the sheer, delicious splendour of clothes that literally cost a fortune. Every season, someone, somewhere writes off the haute couture, sounds its death-knell, and usually describes it as an elderly lady tottering off into deserved obscurity.
But don't wonder yet for whom the bell tolls. Nan flies in to Charles de Gaulle on Tuesday morning to see 'Ungaro, Valentino and of course Saint Laurent,' and everybody who works in couture can breathe a collective sigh of relief. For wherever there is Nan, there will be clothes. -