I just fell out with my best friend for no reason?

In my opinion, she seems like a terrible friend. Whether you want to or not, it's best that you stop being friends with her. Regardless how long you guys have been friends for, people change..and sometimes the change is not good. Also, you went to her about what she did that was hurting you and she didn't seem to respect your feelings? If she can't respect your feelings, she doesn't respect you. She even talked bad about you to other people instead of saying it to your face. I guess it's safe to say, your "friend" is a inconsiderate and insensitive person.