She appeared in the horror film Halloween III: Season of the Witch (1982) as Ellie Grimbridge. Around the same time, Nelkin was scheduled to appear in the film Blade Runner. She had been cast as Mary, a sixth Nexus-6 replicant that escapes from "off-world" and comes to Earth, but budget constraints resulted in her part being cut from the film early in the period of principal photography. Before being cast as Mary, she had done a screen test for the role of Pris but the role ultimately went to Daryl Hannah. Nelkin's screen test appears on Disc 4 of the collector's edition DVD set. Nelkin has made guest appearances in several TV series, including CHiPs, The A-Team, Eight Is Enough, 1st & Ten and Hunter.