One of my closests friends is turning against me, help?

It all started 3 days ago, she was at the ocean with a bunch of guys and one other girl, yes she is a huge flirt. She was texting me from the other girls phone because she didn't have good reception because she was at the ocean. There was a pool party that night and we were going to go together but then I got a text from her that said "well no one wants you to go...ssooo.." and so i just said "Alright? than i wont haha" later on she told me how it wasn't her that said that and it was somebody else, she said it was one of the boys. i belived her because she got the guys to admit that it was them. About 10 minutes before the party ended she texted me "so i hear you talk trash about me" Which honest to god i dont. i answered with "no, i dont. who said that?" she said "i cant say." than 2 minutes later said "it was _____" the guy she said has only been friends with her or about a week and before then they never got along! they always hated each other and just didn't go well together. I dont talk about her, honestly. I said "umm i dont talk to ____.." and she goes "HAHA! lies." i was saying sorry and saying how i wish she would believe me and she just goes "Abby just stop" and "I know you talk sh!t about me and im done" Her other best friend ALWAYS talks so much crap about her and she knows it but she doesn't do this to her! its ridiculous. But wait, it gets so much worse. Last night she had a sleepover with 3 others girls. I'm only friend with one of them and she goes to a different school. She texting me that night at around 11:30 and was like "omg ____ is annoying me so much!" (she was with the girl she said was annoying her but didn't know i knew they were together, she was trying to get me to trash talk her to get us in a fight, b*tchy right?) so i was just like "oh shes really nice" (by the way, i dont like this girl at all, we dont get along. shes a huge jerk. and of course my friend knows that so everything i have ever said to her she is spreading so fast) and shes just like "omg no shes such a *****" and i said "i dont think so" and she was just like "shes like completely ignoring me" and i said "maybe she doesn't realize it, i dont think she would do that on purpose, shes really nice." and she goes "HAHA! Nice, you always say how much you hate her, that explain why you blocked her on fb" (i didn't block her on fb, shes just making stuff up now. its ridiculous!) and i didn't answer, 10 minutes later she texted me "owned." i wouldn't have texted her back at all but i was already texting the girl im friends with that was there, so she knew i had my phone on me. I cannot believe this, i dont know what to do and i need help. shes talking so much trash about me. Shes friends with all the guys because she wears the shortest shorts and push up bras so all the guys want to get with her. Shes in the top 3 prettiest girls in the grade, im in the top 5. So its not like shes dropping me because the guys dont like me and im a nerd. I dont know what to do, please help.