sometimes differences are bound to come up, when some people realise that ur all competing for the same thing...to attract guys (well it feels like that during puberty i guess)...and then we start to judge and just be rude to our friends who we perceive as competition.
ur friend is threatened by you, and the only way she can make herself feel better is by puttin u down. coz by putting u down, she's making herself feel superior. it hurts? of course it does, but you can't do much about it, except ignore it and feel sorry for her, that she is so insecure that she has to bag out one of her friends.
if u confront her, she's just gonna get on the defensive and it won't solve anything.
but if it's something specific that she always says, like "ur such a goody-goody" then ask her, "why is there something wrong with being a 'goody-goody'?" so if u do want to confront her, do it about a specific thing she just said to u, and not a general, "why do u always put me down"
but yeh, dont just concentrate on one friend...u have so many other people to be with, esp. those who are not jealous about ur beauty or success.