Trending: Christie's becomes the go-to haute charity shop

She's a walking fashionplate, a couture-clad collector. So why is Daphne Guinness selling her clothes?

While a wardrobe clear-out for most of us might mean a trip to Oxfam with a couple of binbags, when you're a multi-millionaire and fashion muse, one needs a bit of help to make space in one's armoire.

But that isn't quite why Daphne Guinness, heiress to the beer fortune and granddaughter of Diana Mitford, has donated a selection of 102 of her own dresses, coats, shoes and suits to Christie's, where they will be auctioned next week.

Two years ago, Guinness, 44, halted the planned sale of the late Isabella Blow's wardrobe at Christie's by buying the collection in its entirety. She said at the time that the breaking up of the fashion editor, stylist and muse's belongings would be "carnage".

"It gives me enormous satisfaction," she said yesterday at Christie's, "that my seemingly impetuous decision to purchase the entirety of Isabella's collection is now clearly going to set a few injustices to rights."

The takings will go to The Isabella Blow Foundation, a charity created by Guinness which supports young artists and designers, as well as funding research into depression and mental-health issues. Blow, who died in 2007, is credited with having helped nurture the talents of designer Alexander McQueen and milliner Philip Treacy, among others. Her personal pieces showcase some of Britain's most important designers.

Blow's mantle has been taken on by Guinness in the years since her death. She has been an artist, model, perfumier and designer, among the very small circle of women who still buy bespoke couture clothes from the likes of Chanel, Dior and Balenciaga, as well as supporting young London designers and collecting their work.

Recognisable by her idiosyncratic platinum and black-striped beehive, Guinness dresses in a way that is eye-catching and, at times, a bit gothic. Lady Gaga once described her and Blow as "exceptional icons" and soulmates. But many of the pieces going under the hammer are from her early years, before she had honed her personal aesthetic.

A purple textured A-line coat by Christian Dior, estimated to go for £1,000, was a favourite piece during Guinness's late-20s, while a lemon yellow satin and hide bubble dress by Christian Lacroix was the first piece of couture she ever bought, in 1987. There are several pieces created by Alexander McQueen before his death in 2010 – a pair of black leather boots estimated at £2,500 and two dresses worth around £20,000 each – as well as a pair of Guinness's trademark heel-less shoes by Noritaka Tatehana, which took more than eight months to make. Entry-level prices start at around £250 for a Givenchy dress and a Valentino skirt suit.

The Guinness auction collection is as surprising as it is diverse – given her reputation for extreme edginess, many of the pieces are more accessible than you might imagine, and they show a clear evolution in her personal style over the years, from timeless classics to the more outré numbers.

"The clothes are all by really important designers," says Christie's fashion and textiles specialist Clare Borthwick, "and they embody who Daphne is. Pieces from the big houses are always going to be a good investment, but I always advise people to collect things that they love, because you're going to have to look at it every day and you can't always guarantee what's going to make money in the future."

The funds raised by the sale, estimated to reach £100,000, will also go towards the upkeep and maintenance of Blow's extensive collection, which is set to go on show at the London design college Central Saint Martins, McQueen's alma mater, later this year. "The best thing is that [Blow's collection] can be seen and touched and conserved for the next generation of talent," says Guinness.