Some girl cut my sisters hair at school

My sister just turned 13 last year and shes been dealing with a bullying problem, I havent been able to step in because she goes to middle school and im in high school. Today it got worse when I was with my mom (I'm homeschooling for just the last few weeks of school then going back) and my sister called crying. My mom immediately rushed to the school and took her to a hair stylist after calling me letting me and letting me know what happened. I'm still waiting for them to get home. I'm just really pissed with the girl because my sister has done all she could to make her stop to no avail. I hope if possible my mom and sister press charges. Just wanted to get this off my mind, thank you to the few listening.