The 1958 film Gigi, with a screenplay by Lerner, is based on a novel by Sidonie-Gabrielle Colette. The movie was subsequently turned into a stage musical that was seen on Broadway in 1973. The piece charts the romance that develops between a wealthy playboy and a young courtesan.
Thomas' plays include Indigo, Shamrocks and Crocodiles, Some Singing Blood, and The House of Special Purpose. She may be best known for her writing for the television series Cranford and Upstairs Downstairs.