Like many child performers, Cartwright hit an awkward stage and the acting jobs were not forthcoming. By the end of the 60s, her career had all but petered out so she returned to her native Britain. After nearly a decade, with only one feature appearance (in the dreadful "Inserts" 1975), Cartwright returned to the USA and resumed her acting career with a fresh outlook. Beginning slowly, she made a guest appearance on an episode of "Serpico" (NBC, 1976). Jack Nicholson cast her as his ex-lover in his directorial debut, "Goin' South" (1978). Cartwright then appeared in back-to-back sci-fi classics: Philip Kaufman's remake of "Invasion of the Body Snatchers" (1978) and Ridley Scott's "Alien" (1979). During the 80s, she continued to find interesting roles, notably as the shrill wife of astronaut Gus Grissom furious she can't meet Jackie Kennedy after his space capsule is lost on his return in Kaufman's "The Right Stuff" (1983) and as the town harpy who denounces "The Witches of Eastwick" (1987). By the 90s, however, she could be seen in the unnecessary horror sequel "Mirror, Mirror 2: Raven Dance" (1994) and as the grand dame of a New Orleans family terrorized in "Candyman: Farewell to the Flesh" (1995).
In the 80s, her small screen roles improved. She was wife to cult leader Jim Jones in "Guyana Tragedy: The Story of Jim Jones" (CBS, 1980) and portrayed Ethel Kennedy in the 1985 CBS miniseries "Robert Kennedy and His Times". Cartwright was a reporter covering the presidential campaign in Robert Altman's spoof of American politics "Tanner '88" (HBO, 1988). The actress had her best exposure in the recurring role of prosecuting attorney Margaret Flanaghan in the NBC legal drama "L.A. Law" from 1989-1992. In particular, she was the assistant D.A. who came head-to-head with Michael Kuzak (Harry Hamlin) during the prosecution of Earl Williams (Carl Lumbly), a college professor who is accused of murdering a student he was having an affair with, but was, in fact, found to be not guilty. Several years before the nation got to see Marcia Clark prosecute O J Simpson, they saw Cartwright do anything to get her conviction, including, as it turned out, subvert the law. Cartwright is also remembered as a mother in denial that her daughter was being sexually abused by her husband in "Abby, My Love", a 1991 "CBS Schoolbreak Special". She was the blindly ambitious wife of a vice president who would do anything to become First Lady in the USA Network movie "Hitler's Daughter" (1990) and a local society woman with lustful impulses in the USA Network original "Dead in the Water" (1991). During the 1996-1997 season, Cartwright made several appearances on "ER" (NBC) as the hard-edged mother of a teenager who wants to disconnect from his life support, a role for which she earned an Emmy nomination as Best Guest Actress in a Drama Series.