Help! Copycat friend?

Okay so I have this friend and she is 12 and I'm 15. She just copies EVERYTHING I do. I'm not the nicest person and can be mean. She is starting to act the same way. Our other friends are noticing and are blaming me and getting mad at me for it. And whenever I find something I like, she becomes OBSESSED with it and just ruins it for me. If I say something funny she will repeat it all the time. Shes from a group of friends that I met at outside of school, and she keeps trying to know my other friends from school, which is okay. But not when all she wants to do is meet them and bug me with questions about them. If I tell a story about them she constantly makes references to it. When I say I like something she will automatically like it too. Sure, friends are supposed to have things in common, but not everything. I've tried confronting her about it, tried to get her to like different things. It's just not working! I know she is a lot younger and maybe just wants to be like me? (I don't know understand why, I'm not a great person) But it's not just me that this is bothering. Our whole group of friends is becoming increasingly annoyed with it. Sorry this info is so jumbled, I'm just freaking out and can't take it anymore. Aside from the copy-cat thing she is a great friend and I don't want to lose her because of this little petty thing. Please help me :/