Crosby may be most noted for her role as Kristin Shepard (Sue Ellen Ewing's scheming sister) on the prime time soap opera Dallas from 1979 to 1981 and 1991. Her character is perhaps best remembered for her part in the cliffhanger ending of the 1979–1980 season of Dallas, entitled "A House Divided", that was resolved in the fourth episode of the following season, "Who Done It". In that highly watched episode, J. R. Ewing, (Larry Hagman) was shot by an unknown assailant. Viewers had to wait all summer (and most of the fall due to a Hollywood actors' strike) to learn whether J.R. would survive, and which of his many enemies was responsible. In the summer of 1980, the question, "Who shot J. R.?", was being asked in everyday conversations around the world. Ultimately, Kristin Shepard was revealed to have been the person who pulled the trigger in the classic "Who shot J. R.?" episode that aired on November 21, 1980. It was one of the highest-rated episodes of a TV show ever aired. Crosby's character, Kristin Shepard, later crossed over to the television series Knots Landing in the 1980–81 season. In 1981, Kristin returned to Dallas. Once again the focus of a highly rated cliffhanger, it was revealed in the season opening episode (October 9, 1981) that it was Kristin's body that was found floating in the Southfork Ranch swimming pool. She returned for the Final Fantasy episode of Dallas in 1991, playing the same character had she never met J.R..
^"Divorced - And Living All Alone in an Isolated Farmhouse." Globe March 19, 1991: 46.
^O'Connor, John J. (1980-11-22). "Quotation of the Day". The New York Times. p. 2.47. "No, J.R.'s beautiful wife did not do it. She was too obvious a suspect. The real culprit was her conniving sister, Kristin, the only other character in Dallas capable of equalling J.R. at viciousness. At 10:54 last night, Kristin played by Mary, stepped forward to admit the dirty deed."