Darby was cast in an episode of the NBC sitcom The John Forsythe Show ("'Tis Better Have Loved and Lost", 1965). and as Angel in the two-part Gunsmoke episode "Vengeance." She appeared in the episode "Faire Ladies of France" (1967) of the NBC western series The Road West starring Barry Sullivan and a Bonanza episode "A Sure Thing" (1967) as Trudy Loughlin, guest starring Tom Tully as Burt Loughlin, her father. She also appeared in 3 episodes of Gunsmoke: "The Lure" (1967) as Carrie Neely, "Vengeance: Part 1" (1967) as Angel, and "Vengeance: Part 2" (1967) again as Angel. She was cast in the 1972 movie, The People, which also starred william Shatner, reuniting them from their Star Trek appearance. She also played the unhinged Virginia Calderwood in the first television miniseries, Rich Man, Poor Man with Nick Nolte, Peter Strauss, and Susan Blakely in 1976.