After Asuka attacked Yumi, word got out at Hanzo academy about the incident. Her team turned their backs on her and she was expelled.

Asuka: how dare they? After all I did for them. They went and turned their backs on me? This is all Yumi's fault. She's to blame for my situation. It's MY fault. If I just accepted Peter's feelings in the first place, I wouldn't BE in this situation. I only have myself to blame. If I can't be a good ninja, then I'll have to be an evil ninja and force Peter to love me.