Girls are so cruel. The school I went to, a supposedly good private one at that, one of the girls had a nervous breakdown and one of the teachers did too a few years later, and the crap from the kids at school was what tipped them both over the edge. The poor girl has been in a special care home for the past 20 years since.
I copped the same crap at school and I dealt with it by retreating to a quiet secluded sheltered spot on a step near the science block, and not associating in any way with anyone at school. I'd stick my nose in a book and ignore them all. I got dubbed a huge snob, but I was dammed if I was going to bust my butt playing their stupid social popularity games.
All my friends I knew from out of school. Keeping away from the gossipy bullshit and other kids at school allowed me extra time to study (what else is there to do when ya got no friends?) and concentrate on getting through the part of school that the teachers and government consider more important - the academic side of it. The social side of school be dammed. They could say what they liked and I didn't care because I knew my out-of-school friends were true friends and worth knowing.
I still don't have anything to do with anyone from my school, haven't seen any of them for so long I'm starting to count it in decades now. I refused to go to my school re-union. My out-of-school friends from back then I'm still friends with now, because they were true friends.
What goes on at school doesn't really matter in the long run because once those kids hit the real world they'll suddenly find that all the games they played there just don't apply in the real world. They'll go from being the cream of the crop, top dog, and miss popularity to nobody special, the bottom of the social food chain, the inexperienced runts.
Your daughter has only the rest of this year to go. It's only 7more months. She can survive it. It might be very helpful for her if she can get involved in an out-of-school activity where she can make friends that don't go to her school so she still has some peer support there for her. There really isn't a lot anyone can do about the other girls at school. Physical bullying is easier to deal with, but emotional and mental stuff is harder to prove and harder to stop. The teacher can lecture those girls until they are blue in the face and they won't ever listen.
If your daughter can knuckle down and keep her nose in a book on a sheltered step and ignore the gossip she will get the last laugh, when years down the track the kids that gave her grief have gotten no where in life because they were too busy stuffing around with everyone else's.
And when you're all feeling down about it, watch the movie Romy and Michelle's High School Reunion. It's a daggy movie, but it's a good light-hearted laugh about the exact type of situation your daughter is in where the good girls win in the long run.