Best friend is becoming psychotically bitchy... HELP!?

My best friend and I go to college in down town Chicago. We 2 blocks away from each other and i see her almost everyday.. whether it is my doing or not. The last few weeks have been pretty horrible; i will be extremely nice and she will be rude and condescending for absolutely no reason. Ive told her off a few times but she just gets pissed and starts ignoring me, she doesn't actually take what i say to heart and she doesn't understand that its really hurtful. I definitely have a people pleaser personality and i like to keep the peace in my friendships but this is making me crazy and i cant take it anymore. What do i do? I especially need advice on people pleasing, because i really need to stop doing it.