Power Girl? Superman's once-cousin, but that continuity was wiped out, now she's an Atlantian sorcerer or some crap, wait, no, now that entire continuity is back and she's Superman's cousin again? That Power Girl?
Look, I don't think audiences are as stupid as Hollywood, but if you try to throw that into a movie, you're asking for trouble.
Superman's cousin is Supergirl. And we only need one S-Shield in this movie.
Unless you want to bring back Shaq as Steel.