I am so sorry, as it breaks your heart. My dd24 is a 4th grade teacher and she sees bullying every day. It makes her sick how mean kids can be. Last year she had 6 mean girls in her class, they were pulled out once a week by the social worker for counseling, because they were so bad. It was horrible, not sure if it even made a difference.
I hope you have spoken to the teacher, principal, social worker, and if you have to the superintendent. I would keep all lines of communication with her open so she can discuss everything with you. She needs to have someone she can trust.
I had a friend who was a principal/superintendent at a junior high, and he told me at that age kids are vicious. He said "If your kid get out unscathed, then you are good." How sad is that, and he told me this about 15 years ago, so nothing has changed. Remind her that in high school there is more diversity and you are less judged for who you "are". Hang in there mom, you are doing a good job!!