Alright I think I get it, in a crisis or say in a battle Ancia could call upon her newly found inner leader to basically give her great confidence, insight, and anything else that makes up a great leader. She hasn't truly changed really, in everyday life she's still as before.

Edit: Anyway I only have one more real question, with her transformation powers what counts as a heavy magic drain, how drastic do the changes need to be for significant magic usage.