Wow. Good that you've found out and can try to address it.
Because other parents aren't sorting that out, could you not take a really fancy packed lunch, so she joins in?
Oh jesus. You have a support worker at the school, maybe contact them and tell them about your daughters lip and the threat...
Sounds like a good plan (I also have a feisty daughter who is 10). I don't know where you can get help, so I'll follow this thread in case there's something I can learn too.
Same as ours, although ours hasn't gone 'way beyond' yet.