Can you take someone to court for harassment/bullying?

[Concerned MOM]

I have a child who is being harassed & bullied through Twitter & askfm website by a bunch of schoolmates & other kids from other school. One of the girl's from school has threaten to punch her last year via twitter & the next day when she went to school, all the kids from school knew about this argument & all were ready to video the fight, according to my daughter. Since then, they've made up but now, this group has started again with my daughter for no particular reason. They have been posting on twitter that my daughter is a lesbian. I have just reported this incident to the school but it seems that it is getting worst. More & more kids are now harassing her & calling her a snake. I do have evidence & took snapshots of the twitter page where they've posted it. I need to put a stop to this matter.