Theaker guest-starred as The Caterer in an episode of the first season of Curb Your Enthusiasm. Theaker then guest-starred in the third season of the acclaimed sitcom Husbands.
Since 1987, she has played roles in various television shows and movies, including The Kids in the Hall, Joey, Howie Mandel's Sunny Skies, Desperate Housewives, Rat Race, Entourage, Bones, and Lemony Snicket's A Series of Unfortunate Events as well as the Stargate SG-1 season-eight episode entitled "Citizen Joe." She is a member of Christopher Guest's cinematic repertory company and has appeared in four films and multiple commercials for Guest.