this person did more than just misbehave, she was abusive and physically assaulted you.
i have never done group stuff but doesn't the group have rules and wouldn't this be grounds for her being thrown out of the group?????
i don't know anything about US law and other things but if you don't feel safe around her, couldn't you can take out a restraining order, then she won't be allowed to attend.

it is not good enough how the therapists are treating this. it isn't just you being overly upset about a minor thing, it is physical assault which you could lay charges for.