My so-called "friend" is doing everything I am doing for her to become better than me.?

So I have this "friend" since I was in 10th grade. She always wants to be with me even though I don't really want to be with her that often. But somehow, as time went by, we became close with each other together with some of my other friends. So later on we had this circle where I and her belong. Since then, she has been doing and imitating everything I am doing, asks questions and asks for help in different school works, etc. Since I used to think we really were friends, I helped her. But eventually, after a while, I felt as if she is just using me to get her grades higher, or worse, become better than me. Throughout 10th grade, our average grades were very close with each other and after 10th grade I was the top of the class and she was the second. Now, I really think she is already trying her very best to become better than me and overlap me by using me. Lately, since I was in a different section, when I ran for president in my section, she also ran for the same position in her section and we both won in our respective sections. Also lately, when I ran for a position in the student body, after like a day or two, she also ran for the same position. Everytime I am campaigning, she is always by my side even though I am already avoiding her so that she can also approach the people I'm campaigning. So again, we both won. Now, I just discovered about an hour or so, that she also enrolled in the same tutoring school I was enrolled in so that everything I will learn there, she will also learn. I am really pissed on her already. I decided to really completely stay away from her but if I do, I will also sacrifice my other friends because I will have to stay away from them. So I would just like to ask, what should I do to stop her from always imitating me? I am afraid to tell her directly because I know she will make rumors about me. So I really just need help from you guys. Thank you in advance!