Supergirl is Supermans cousin and is first brought to life in DC comics. Her back story is that she was sent to earth at a 13 year old supposedly to look after the baby  Kal-el but her ship was knocked off course and she spent 24 years in the Phantom Zone before finally making it to Earth.  We were lucky enough to meet Helen Slater who starred in the 1984 film and she was absolutely lovely and thrilled with her little character.