what should I do?

Lisa
So well I have a classmate and she always copy my test answer or tried to copy me or anything like that. And I didn't really mind that but then, she started to steal my stuff that is very important for me and my friends and also she stated to try to be like me like everything that I do she do it too like everything that I say or when I take a selfie or picture or anything like that and I was still okay with that but it went worst. She is starting to steal my friend's stuff and she is starting to bully another person and I know that for bullying maybe it is nothing to do with me but, I think that she is maybe confused in herself or not confident in herself so if you can, can you give me some advice or tell me if you had or have  like this problem what would you do?