What would you do if your 14yo nephew had a crazy gf trying to get rid of you?

She's 15yo & my nephews 14. And IM 17. My nephew & I have been bestfriends ever since he was born, literatly. He's like a little brother to me. & about a year in a half ago (maybe less) he started going out with this girl. Well, she plays the role of "goodie two shoes" and is acting sooo fake. Shell put on a fake smile, call me beautiful, bring cookies & candy over, etc. All nice & sweet. Well recently, she tried making me break up with my bf. Saying "oh he's ugly, not good enough for you, I don't like him @ all, don't trust him one bit." a week later the little whore decides to add him, he denied her request on facebook, and she sends him a message acting like she's his bestfriend. So I go to my nephew, mad of course, and told him that I don't trust her talking to my bf. Next thing I know, she calls me outta the blue, a few days later (on Monday) at 2am cussing me out, saying I'm a sh*t talker, I'm fake, she "knows what I'm trying to do"!?! She doesn't trust me, she hates me, and that I'm mental & that sooner or later, I'm gonna get fuc*ed up. Oh, and that she knows I don't like her. Well first off, I told her I had nothing against her, & I wanted no problems. & now this little.. Psychopath, apparently grew some balls all of a sudden & is threatening me. Now, I'm purteo rican & italian, my temper is.. Beyond bad when someone pisses me off. I see this girl on saturday. & I don't want to hurt her physically.. So WTF do I do bro!?people are telling me to play by her game, but I know if she says something wrong, which I know she will (cuz clearly she loves to piss me the flip off), her heads gonna be bashed against the wall. She really went over the edge this time. & I need help. Fast. I wanna do something that'll make her go crazy. I wanna make her have a reason to hate me. I want her to break. & show everyone her true self, including my nephew. Cuz even though I recorded what she said, he doesn't believe me. Please.Help. Btw, she abuses him. This needs to end. Please