De Castellane joined Chanel in 1984 where she started as a studio assistant. Creative director Karl Lagerfeld soon asked her to oversee the development of costume jewelry designs. Over the 14 years[2] she worked at Chanel, de Castellane remained a vibrant inspiration for Lagerfeld, bringing her fashion playfulness to the costume jewelry, layering it with cartoon and pop-culture references.[2]
Of de Castellane, Lagerfeld commented, "She follows the rules I like best in life: Don't compare. Don't compete. You look at her. You get the message."[4]
De Castellane sometimes appeared on the Chanel catwalk modelling the house’s collections