How can I deal with a dramatic best friend?

One of my best friends is such a drama queen. We get into fights a lot, and she always thinks she's right. She acts like our arguments are all my fault, and when I try to tell her they're her fault she won't listen to me and she gets madder. She's almost a year younger than me, but we're in the same grade, if that makes a difference. I'm almost thirteen. She can be really rude. One time she told me I was emotional and said that the way I painted my nails was childish. I really like this guy and talk about him a lot to her, but she gets mad and says that he's more important than her. She never understands. I've tried to stop being her friend but it doesn't work because she follows me around and tries to talk to me. And plus, all of my other best friends are friends with her too. It's like I can't get rid of her. There's this other girl that I've known since third grade, and we're really close friends. In September last year, Madeline (the drama queen) and Alexandra were best friends. Then they started getting mad @ each other for stupid reasons. Both of them complain to me about each other and Madeline kept bothering me and asking me why I wasn't on her side, when I had told her over and over that I wasn't choosing a side. They get in a fight then a few days later they're friends again. I can't even keep up with it. Madeline gets upset whenever I try to make her understand that I don't like something she's doing. She told everyone I ruined her sixth grade year, just because of an argument we had. The last time I tried ignoring her, she followed me around all day and kept begging me to forgive her. She kept calling me over and over when I didn't answer my phone. How can I deal with her being like that?