In addition to serving as muse and constant companion to Yves Saint Laurent, de la Falaise designed accessories for the iconic French house. As Cathy Horyn writes in her On the Runway post remembering de la Falaise, her “chunky bracelets and necklaces…helped establish the YSL look.” After Saint Laurent retired in 2002, de la Falaise launched her own ready-to-wear line, sold in a namesake boutique she opened on Rue Cambon.
La Falaise moved to New York City in the late 1960s, where she briefly modeled before turning to designing printed fabrics for Halston. Eventually she moved to Paris, where Yves Saint Laurent became a close friend and employer. She became one his muses, joining his firm in 1972, where she designed jewelry and hats and inspired him with her inventive wardrobe: "one week she was Desdemona in purple velvet flares and a crown of flowers, the next Marlene Dietrich with plucked crescent-shaped eyebrows".
In 2002, La Falaise began producing her own clothing and jewelry designs. As reported in The New York Times by fashion writer Cathy Horyn, "The clothing line captured much of her rare taste—well-cut blazers in the best English tweeds, French sailor pants in linen, striped silk blouses with cheeky black lace edging, masculine walking coats with fur linings, and gorgeous knits in perfectly chosen colors".She also designed cloisonné boxes and porcelain vases for Asiatides, as well as jewelry for the boutique of the Majorelle Gardens in Marrakech, Morocco. Her two shops in Paris, one of which was designed by her brother, Alexis, are called Loulou de La Falaise Fantaisies