Help!!!!! What should I do?

Okay, I have this group and this girl in my group (Let's call her girl1) told this other girl (girl2) that she isn't allowed in our group anymore because she's 'too fat'. I was outraged by girl1 so I told her: "Who made you in charge?! You can't just kick people out!" She got sooo mad with me and later on, I was one Msn & a few of my friends told me that she was telling everyone on msn to block me and hate me...

The next day I went to my group and sat down with them but girl1 told me to get lost and go to hell so I told her that she can't tell me what to do but then she kicked me & slapped me, she tried to punch me but she missed, I didn't hit her back but then girl2 pushed her over and kicked her... Now girl1 told the principle and blamed it on me that I bashed her up, but I didn't even!!!! The principle won't listen to me!

I can't tell on girl2 because that would be sooo mean and she stood up for me... Now because I catch the same bus as girl1, she always tries to start a fight with me, none of my other friends catch that bus... I don't want to fight her, I'm too scared, even though I have girl2 (who is really strong) on my side, I don't want to!!!

Please help me!! I DON'T KNOW WHAT TO DO!!!

(Btw I'm a year 7)