Her greatest triumph was the Proust Ball in December 1971, in celebration of the centenary of the reclusive author's birth. Some 350 guests sat down to dinner, with 350 more for a late supper in the dining room, bedecked with palm trees and ferns and squares of trellis. They ate consomme, quenelles of lobster, duck stuffed with foie gras and foie de canard, decked with pineapple, small mirabelles and a delicious prune jam The feast ended with pistachio bombe glace, and it was all served on pleated mauve table cloths, adorned with mauve orchids. Torches lit the way to the chateau and chandeliers hung out of the windows.
The guests came in costume and were photographed by Cecil Beaton, adorned as the photographer Nadar. Beaton set up a special studio for the occasion, taking portraits of Marisa Berenson as the Marchesa Casati, Audrey Hepburn, Princess Grace of Monaco and Elizabeth Taylor. The Duchess of Windsor, described by Beaton that night as "a mad Goya", was bedecked with a large blue feather. At dinner, as she turned her head, the feather dipped into the consomme or gravy and then brushed Baron Guy across the face.
In 1972 there was a Surrealist Ball at Ferrieres. The pudding was a life- size model of a woman, naked but for a rose, lying on a bed of roses, the whole thing made of sugar. The invitation was printed back to front, the reversed writing transposed on to a sky by Magritte.
Described as a legendary hostess whose name was the password among le tout Paris, the Baroness was also a considerable fund-raiser for medical research, and a patron of artists, musicians, movie stars and couturiers.
She could also take credit for the advancement of an employee of Rothschild Freres, contributing to his later success in politics. Baron Guy chose to keep his business and private entertaining strictly separate, his business friends being restricted to a shoot a year at Ferrieres. One year one of the guests was the manager of Rothschild Freres, Georges Pompidou. In the words of Baron Guy, Marie-Helene "immediately detected the amazing richness of the human being behind the man who arrived for his first weekend, a bit awkward, reserved to the point of shyness, moreover a businessman (a priori suspect), uncommunicative . . ." Marie-Helene's mother described him as possessing "one eye a vicar's, the other a rascal's." Pompidou became a close friend of the Rothschilds. He had already worked for de Gaulle. The dual influence propelled him forward.
Later Baron Guy took credit for Pompidou influencing de Gaulle in France's entry to the Common Market. "Pompidou had become `European' as a result of his experience in working at the rue Laffitte".
Marie-Helene was the daughter of Baron Egmont van Zuylen, a rich diplomat from one of the oldest families in the Netherlands, in the service of the King of the Belgians. Her mother was Egyptian. Her father owned the magnificent Chateau de Haar in Holland.
Marie-Helene was educated at Marymount College in New York, where she considerably developed the spontaneity she had inherited from her mother. Following graduation she came to Paris and married her first husband, Count Francois de Nicolay, a breeder of thoroughbreds in the Sarthe region. They had one son, Philippe, and shortly afterwards divorced.
Her second husband was Baron Guy de Rothschild, head of Rothschild Freres, the largest private bank in France, but later nationalised. They met at a gala in Deauville at which Edith Piaf provided the cabaret and he presented the prize of two cases of Chateau-Lafite to the Nicolays. The Baron was much struck by the young countess. Eventually they were married in 1957.
For him too it was a second marriage. The union was controversial because the bride was Catholic and he was Jewish. She was obliged to obtain a papal dispensation to annul her previous marriage and remarry outside the faith. He was forced to relinquish the presidency of the Jewish community in France. This was the first non-Jewish wedding for a head of the Rothschild clan, though, interestingly Marie-Helene's grandmother was the daughter of Salomon de Rothschild, Guy's great-uncle. Their son, Edouard, was raised as a Jew.
The Baron described his wife as having "a fabulous appetite for life, emotions always at their height, a spontaneity with a thousand facets, as ever-changing as the sea. And charm, which defies description." Rostropovitch, the cellist, said that she had a heart "that was bigger than all Russia". Richard Burton and Elizabeth Taylor were great favourites in the late 1960s. His description of Marie-Helene was sharper than most: "She is quite an ugly woman with a large hooked nose and an almost negroid mouth but very beautiful blind eyes, and the vivacity of her manner and her machine-gun delivery in both languages makes her very attractive."
She was indeed rather gaunt. The explanation was that she was a sufferer from arthritis from as early as 1962. Her husband wrote: "It may seem incredible that her exuberance is all too often shattered by pain." Lately her illness confined her to her bed for some years.
The de Rothschilds were both keen race-goers and breeders (with 50 mares at stud). She had her own colours from 1953. Their horse Exbury won the Arc de Triomphe and the Coronation Cup. Shantung came 3rd in the 1959 Derby, and Baron Guy won the Eclipse Stakes with Tropique. His best horse, Vieux Manoir, won the Grand Prix de Paris. The Queen visited the Rothschild stud privately on her visit to Normandy in 1967.
They restored the family chateau, Ferrieres, and reopened it in 1959. The property dated back to 1855 and was designed by Joseph Paxton, the architect son of the Duke of Devonshire's famous gardener. It was hailed as "the finest example of Second Empire style". King William I of Prussia declared: "What an incredible palace! A king would not have dared to build it. It took a Rothschild!" Almost all the Rothschilds lived in a manner dubbed the "Rothschild style" - a mixture of Napoleon III objets d'art, comfort and luxury, with precious miniatures and rare books mixed in with family photos, plants and flowers. Eventually in 1975 the Rothschilds gave the chateau to the University of Paris, and settled in a smaller house on the estate (of which, after initial reluctance, Marie- Helene eventually became fond).
They also lived in the historic Hotel Lambert on the Ile-Saint-Louis in Paris, where their great friend Alexis de Rede had a splendid apartment. When the Hotel was for sale in 1975 Marie-Helene persuaded Baron Guy to buy it: "Do you feel young? . . . Young enough to change the course of your life in the space of two hours?" They restored the palace to its 17th-century glories.
In 1981 President Mitterrand nationalised all the French banks and for a time Baron Guy went to live in America, but Marie-Helene remained at the Hotel Lambert.
A life such as hers could scarcely be relived in the 1990s. In Marie- Helene the Rothschild fortune was more than matched by imagination, inspiration, supreme good taste and generosity. She was like a child in a dream-world and opened its possibilities to many who will never forget it. Baron Guy recognised this in the dedication of his memoirs: "To Marie-Helene, without whom things would only be just what they are."
Marie-Helene van Zuylen de Nuyvelt, patron of the arts and racehorse owner: born New York City 23 August 1931; married first Count Francois de Nicolay (one son, marriage dissolved), 1957 Baron Guy de Rothschild (one son); died Ferrieres, Seine et Marne, France 1 March 1996.