Bullying in and of itself is not against the law in most places. It is against most school policies. However, that does not mean that if someone is hit or stalked that it is not actionable. It just means in most places, there is not crime called "bullying". You do not provide any context. Is it at school? You tagged "cyber bullying"--some schools have rules on this even if it is not done on school grounds.
Obtain the school/school district's written policy on bullying. The school is obligated to follow it and investigate. However, if their investigation does not turn up anything actionable in their opinion, they are not obligated to act further. Educational Rights attorneys are specialists at dealing with schools, so if you can hire one, that would be ideal. Use the "find a lawyer" tool on AVVO.
The police should be called every time your daughter is threatened or hit or stalked by the other kid (and each incident should be reported in writing to the school). Also, as long as the other kid is a minor, her parents are responsible for her actions if they know, or should know, of this propensity. So get a local lawyer to send a legal letter to this kid's parents--that'll be proof that they've been put on notice. Then, you can sue the parents for everything their kid does. Perhaps the attorney's letter will get their attention.
The lawyer can also advise on getting a restraining order. Schools tend to be afraid of that because then they have to monitor and keep them apart.
The legal letter to the parents, suing the parents, restraining/"no contact" orders apply even outside of the school context. Obviously, get your daughter off any social media and block any and all numbers and email addresses you can.
http://www.tbi.state.tn.us/cyber_crime/cyber_crime.shtml This link is to the TN state agency that addresses cyber stalking and other cyber crimes (as well as other crimes)
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