Jeanne Bal played Nancy Crater, the form worn by the shape-changing salt creature and seen by McCoy as his lost love, in The Man Trap.
Jeanne Bal (1928–1996) was an American actress who worked on Broadway and in television comedy and drama. In The Man Trap she plays the principal version of Nancy Crater, the woman McCoy once loved.
The real Nancy is dead, and what the landing party meets is the last creature of M-113 in disguise. Each man sees someone different. Bal plays her as McCoy sees her, apparently unchanged in a dozen years, and also in the greying, older form perceived by Kirk; a younger blonde woman seen by Crewman Darnell was played by another actress.
In the final scene the creature, in Nancy's shape, attacks Kirk in McCoy's quarters, and the doctor is forced to kill it.