I guess that staff gives her a pretty significant strength boost to go with all that magic? Casually flipping around a sword that was too heavy for the King's knights to lift. And the best part is she probably doesn't even realize it.
I think it's supposed to be either the negative speed or the mp drain for the skill, that make the sword unusable by other people. She get's a plus 300 to her speed from her boots and the Staff has a mana stock of all 9s, so neither negative effect works against her.