When you say Marion, do you mean Marona? (the main girl with green
hair who summons the phantoms). She levels fast in my game too, but
its not a problem. It's better that she become hard to kill so that
you never get a "Game Over."
I've heard some games where she levels extra slowly too, I think it
depends on whether you have her kill enemies or not. Marona knows a
lot of heart attacks in my game, so she is kind of good at killing
enemies. Mostly she used blinding light and energy ball, but she also
knows revive which helps a lot.