There were the shrunken T-shirts, cutoff jeans and espadrilles she favored. There were the babydoll dresses that few besides the actress Mia Farrow ever wore with greater élan. There were the striped Breton sweaters she helped popularize. There was the dress crocheted with see-through daisies she once wore to a French arts union gala, one whose plunging neckline was strategically, if barely, fastened with a brooch. There were the ragged bangs that she maintained all her life and that looked as though she’d cut them herself with cuticle scissors.

“Her style was very different from American style,” Ms. Sui said, and it introduced “something new to our fashion vocabulary.” What exactly was it about that style, the designer was asked? “There was something British about it, that slightly rumpled English look but fused with the classic French codes,” she said.

Perhaps, in the end, the Hermès Birkin bag provides the best example. Before its invention, Ms. Birkin was often photographed toting a straw marketbasket crammed with makeup, keys and assorted paraphernalia. “I was well known for carrying a basket,” she explained in a 2018 interview on YouTube. “So I obviously knew girls liked to have masses of things in their handbag.”

It was her bulky basket and its overflowing contents that caught the attention of Jean-Louis Dumas, the chief executive of Hermès, on a flight from Paris to London and inspired him to create a tote capacious enough for all her stuff. “I would love to have been a sort of neat person and wear a Kelly,” Ms. Birkin once explained, referring to a prim, boxy-style handbag created and named for the film star Grace Kelly. “But I never thought you could get enough in it.”

The satchel-style Birkin, made from supple leather, was based on an earlier design, the Haut à Courroies, created by Hermès around 1900. With its loop handles, closed with a strap fastener anchored to a signature hunk of hardware (and typically left unlocked to display the Hermès logo), the bag became a globally recognized emblem of status and wealth. With a base price of over $10,000, Birkins remain infinitely covetable and customizable (a Diamond Himalaya version became the most expensive handbag ever at auction when Sotheby’s sold it in 2022 for over $450,000) and are worn and collected by celebrities such as Kim Kardashian and Kylie Jenner, whose handbag closets constitute a subset of online fashion pornography, as well as Jennifer Lopez and Cardi B.