FindPeace, you are not responsible for your T's safety, your T is. You should not terminate therapy. Your bully alter is not the only one in charge and you can't know what will happen in the future. It's good you/your friend told you T about the situation so she is aware of it but you cannot "protect" other people, that's their job.

Think about it logically; if you give in to your alter here, what more might she suggest and think she should have/be in charge of? Keep some of the power for yourself, don't give it/give in to your alter or you can never get out of the mess.