A friend of mine is writing a story. She told me generally what it will be about, and I said that it reminded me of something I had seen before, but I couldn't remember the exact story. Her response was "hm.. don't think i've seen that 1.. i hope i'm not too derivative, cause that's only the base plot." The story went something like this (I think it was a DC Comics animated episode):

A superhero is working with a group, maybe the Justice League. She has something like an amulet or a shield, in which her evil father is imprisoned. He keeps ordering her to release him, but she knows that if she does, he will destroy the Earth with his powers. Keeping him imprisoned is a strain on her. Finally the group she's part of begins a battle with a supervillain who is about to defeat them. In desperation, she releases her evil father from his prison to fight the supervillain. I don't recall the ending, but possibly her father sacrifices himself to kill the supervillian.

Does this story ring a bell with anyone?