My Stepmother is an Alien - 1988

Trying to save her home planet from destruction, a extraterrestrial named Celeste arrives in the world and begins her research. She woos unique scientist Dr. Steve Mills, a widower with a daughter. Before Celeste finds herself in her life on the planet along with love with Steve, where she experiences intimacy for the very first time. But when she loses sight of her assignment, she starts to wonder where she belongs.