What's wrong with my "bestfriend"?

My bestfriend is a such a NEGATIVE person, she hates to be nice to people, she actually said it " i hate being nice and giving compliments it makes me feel mushy " And she's being awfully awful lately, as soon as I walked into school she started acting so bi*chy, and today, we were outside for gym cl and these mentally handicapped people walked by and i was like " I'm going to open help them bring in the things from the car " and she was like " let the metals do it " and me and my other friend were like " That''s soo rude, don't say that, it's not nice " and she wouldn't talk after that at ALL. For the rest of the day, when recess came I came in the clroom from downstairs and I was like " Get any work done :) ? " ( with a bubbly tone in my voice ) and she slammed her laptop and said " nope! " ( rudely ) Then at lunch I tried talking to her, I asked her questions and she wouldn't even answer me.. I followed her to the gym because I wanted to know what was up, I'm not just letting her treat me like shi* without an explanation, because i haven't done ANYTHING at ALL to her, I'm a way better friend and more nicer then she is to me, and she didnt say anything she just kept walking with this pissed look in her eyes and I was like " You have no right to treat me the way your treating, ok, fine be like that i dont' really care? " and then i walked away... Then she STILL wouldn't talk to me for the rest of the day? I'm pretty sure she's mad that I called her out on calling those people " mentals " I'm getting really sick of her attitude. But two people can play this game, I'm not going to talk to her, I tried being the bigger person, obviously didn't work.. And when she finally comes to her senses that she's LOSING me, I'm STILL not going to talk to her, because she has NO right to treat me like shi*t for NO reason. Or just because she wants too. She's brining me down and making me mad and I HATE being mad.. Please help? :(