What should I do about my friend who keeps haring me?

I am 12 years old and going into 7th grade. My friends and I go to a daycamp thing, just to keep us from being bored all summer. So there's this issue with this boy a grade younger than us. My other friend in his grade used to like him, so I was trying to get him to like her by texting him. She stopped liking him, but we were still texting. Then he lost his phone, and everyone thinks we were going out! Now everyone thinks he hates me and I like him, a lot! I don't like him and just joke around about it. So this one friend I have, let's call her Kristie, keeps talking to him at camp about me, telling him the most random things! She tells him I want to have a with him and this other kid, and that I want him to take his clothes off and stuff like EWWW! I just ignore it or slap her. So once today I was running away from her cuz she was gonna slap me or something, and I fell in the mud lol and got all dirty. I didn't care, like we were laughing, but I told her she HAD to stop talking to the boy about me, and stop haring me. Then she told me later that she was crossing her fingers when she said she wouldn't talk to him! I mean how childish is that! And what kind of friend would do that! So now she keeps hitting me, and showing him embarring pictures of me and it's starting to get me reeeaaalllyyy mad! What should I do, this girl is crazy!