Very bad friend problems?!?!?

One of my best friends suddenly started being so rude to me, calling me a b**** and saying "I've changed (and that all my friends agree)" and that I talk s*** about a girl that I hang out with, which is a complete lie. She is being so rude to me and ignoring everything I say and she doesn't believe me at all- like I don't know what I said. I had some super fun times with her and I don't want to lose her friendship, but how can I talk to her when all she will do is yell at me and make up false accusations about me? Please help...