What can you do when a girl is trying to ruin your relationship?

Okay, me and my boyfriend are both 16. We have been dating now for almost 7 months. We're happy together. We don't really argue that much and we both respect each other. Back when my boyfriend was in the 8th grade he talked to this girl. He never dated her, just talked to her. She is now trying to ruin our relationship. My boyfriend never replies back to her. But she ALWAYS sends him texts, pictures, dirty pictures, messages on facebook, she always tells him she is coming by his house later, she'll text me and tell me the same thing. It's so stress full to think that she actually might. Like trust me when I say this, she is crazy. She could easily go to his house and mess with him. Like she is insane. She has thrown 3, as of last week, glass bottles in my driveway saying she is going to have sex with my boyfriend and that she is going to steal him away from me. I know for a fact that my boyfriend would never cheat on me, especially with her because he hates her. I always ignore her when she says things to me but he will text her back cussing her out and telling her how stupid she is and how much he hates her and stuff. And it just seems to only get worst. It's causing so much stress on me and our relationship. And I told him that if it doesn't stop we just can't be together. I love this guy, but it's way to stress full with her always in the way. She talks about us constantly on facebook. Like I've seen her post on friends walls about our new pictures and how I look terrible or how she would look so much better in his arms. Like she's seriously obsessed. And I don't want to break up with my boyfriend because of her problem. But I want to know what can I do? My mom literally told me to beat her a** and then she'd stop. But I'm not the type of person to fight. I'm really calm and mellow and I'd rather solve a problem by working it out rather than fighting. But if there is nothing else to do, I will. I mean I've tried talking to her. I've told her in a calm way that my boyfriend doesn't want her. And if he did he would have dated her 3 years ago. That he's with me now and he's happy and if she really cared about him she'd leave us alone and let him be happy. I don't know what to do. What can I do in a situation like this?