Gee, people are shocked and upset by antagonists having their own motivations and reasons for doing horrible things? I think she's a fine character. No good villain realizes they are the bad guy. She isn't some unrepentant evil. She is a kid with lots of magical power and it went to her head. She saw herself as the heroine of the story, one who will ascend to be like Hero Girl, so at her core she won't have to see her friends die.
Her bullying makes sense as she could see Gale as to weak to be an adventure, and so should leave for his own good and escalated more and more until he was expelled. She also sees her reputation as a key part in protecting her comrades, so losing it makes her fearful and angry, and as an oh so "mature" teenager, she lashes out.
If you want to blame someone, blame their society and school for failing to instill proper guidance into these kids who are being trained to fight with powers which are beyond an average person.
And Gale also wants to be like the Hero Girl, and so even if someone was bad to him, he will help them out. He could probably get Amoracchius with his loving nature.