I don't know if there was ever an official origin for SuperGirl that stuck ( Personally, I like the 90's Superman series version)...... but could a new movie on that part of the franchise work? The old one, from what I Remember of it, was REALLY sappy...and just plain sucked. The only thing good about it was Helen Slater, who looked really great in the outfit. I think a fun outing for the new one would team up Super Girl and Bat Girl. Instead of having them fight a female villain, pit them against Lex Luthor and the Joker and see how well it goes .