Power
Power is not entirely wrong, but she does think too highly of herself. She is undeniably a pivotal figure in the show. Most importantly, unlike many Devil Hunters, she enjoys fighting rather than seeming cowardly, making her even more of a menace to her opponents.
As a Blood Fiend, she is free to experiment with blood in any way she pleases. Her most notable attack is the creation of blood-hardened weaponry. We've seen her fight quite a few times by this point in the series, but we haven't yet seen her in her full Devil form, which is far more powerful.