She is best known for her role as Robin Maxwell on the 1983 science fiction miniseries V (replacing Dominique Dunne, who was murdered while the show was in pre-production), the 1984 sequel V: The Final Battle, and V: The Series.
Film roles include Pat Bernardo in Fast Times at Ridgemont High (credited as Blair Ashleigh), Three for the Road with Charlie Sheen, A Sinful Life, Inside Monkey Zetterland, Fright Night Part 2, S.F.W., and Dream Lover with James Spader.
In The Anniversary Party with Jennifer Jason Leigh and Alan Cumming, Tefkin also performs an original song, "If Your Love Is True".
Lucie Gamelon was a fixture on the L.A. music scene and played major dates on the 1998 Lilith Fair tour sharing the stage with Patty Griffin and Morcheeba among others.
In 2004, Tefkin performed her one-woman show In the Land of the Giants: A Tragicomedy With Music at the Blank Theatre in Hollywood which the L.A. Times described as "witty, poignant and often hilarious."