You should first ask her what does she want and why is she doing? Is she mentally fine, what all she thinks, may something is annoying her or there could be the other reason. This can only be resolve by talking to one another. If she continues further then you can talk to her parents that these type of activities are done onto me. And ask them to make her understand she is doing wrong. If her parents also support  her then you can go to police station and can file a complain, don\’t delay further because taking action is very important; you don\’t then this will cause harm in your physical  and mental health.