A) She's not going to stop, trust me on that one. She feels inferior and right now you're her drug of choice in that department.
B) Why do you want a friend who competes with you and basically doesn't have the capacity to be happy for your achievements? Doesn't sound like a friend to me.
C) If I were you I'd cut her loose, but that's just me. I like to be on an even playing field with my friends, and not necessarily in the superficial sense i.e. what we have, but rather, sharing the same definition of respect. I don't see any respect on her part, you can't truly respect someone you feel is superior or inferior to you because then it causes some sort of subconscious power struggle. Not good.
DD 11.24.07 DS 9.8.09
Unless you have a degree in putting yourself in someone elses shoes, you have no idea what other people are experiencing in this world.