Based on the DC Comics character, Supergirl follows Kara Zor-El as she travels to Earth after a powerful Kryptonian energy source falls into the hands of a dangerous witch. Starring Helen Slater alongside Faye Dunaway and Peter O’Toole, the film combines superhero adventure, fantasy elements and 1980s comic book spectacle within the era of the original Superman film series.

Från IMDB:
After losing a powerful orb, Kara Zor-El, Superman's cousin, comes to Earth to retrieve it and instead finds herself up against a wicked witch.