My sister was like the girl who's harassing your daughter. My parents, however, are probably not like hers. My sister beat up a couple kids (one was handicapped) so my parents took her out of school because they didn't want her to hurt anyone else. If she had, the school would've been liable (a point you might want to bring up with the school) since they knew she was dangerous to other kids. Turns out there are special schools for kids like my sister and the school district has to pay for it. My sister now goes to a school where there is a counselor for every student and they can use restraints on the kids without calling the parents. My folks love it. I hope things work out well for you and your daughter.
In life's small things be resolute and great
To keep thy muscle trained: know'st thou when Fate
Thy measure takes, or when she'll say to thee,
"I find thee worthy; do this deed for me?"
Nemo me impune lacessit.