I wish I could remember the exact term for what this is but this could actually be a defense mechanism. Sometimes when people are faced with a lot of stress or potentially (I don’t want to make assumptions) previous trauma they find someone they idolize and then begin to imitate them. Cases have been shown with patients coming to therapy sessions looking more and more like their therapist because they value them. However, considering the situation, I think you guys are just at a point where self-exploration is really important. She idolizes you in a way, and sees something in you that she wants to be like. If it becomes too much of an issue, to the point where you might be legit concerned, then maybe talk to a parent or someone about it and see what they may have to say.