Crosby's first high-profile role was as Lisa Davis on the soap opera Days of Our Lives. She has appeared as Dr. Gretchen Kelly in three episodes of Lois & Clark: The New Adventures of Superman, and as a sheriff on The Adventures of Brisco County, Jr. episode "No Man's Land". In the early 1990s, she played the role of the mayor in the short-lived series Key West. She also appeared in two episodes of the cable television series Red Shoe Diaries, playing a different character in each episode. Crosby had a small recurring role in Aaron Spelling's prime time drama, Models Inc, a spin-off from Melrose Place. She was a guest star on the eighth season of The X-Files for two episodes, in which she plays a doctor who examined Agent Scully's baby. In 1991, she was a guest star in "The Deadly Nightshade", a first season The Flash episode as Dr. Rebecca Frost. In 2006, she was a guest star in Dexter as Dexter's first victim. Crosby had a recurring role in Southland as Detective Dan "Sal" Salinger's wife.
The character first appeared in the series' pilot episode, " Encounter at Farpoint ". After Crosby decided to leave the series, Yar was killed in the episode " Skin of Evil " near the end of the series' first season . She was written back into the series for a guest appearance in the third season episode " Yesterday's Enterprise ", in which her character was still alive in an alternate timeline, and again in the final episode of the series " All Good Things... ", which included events set prior to the pilot.