How to get her to stop freaking out about this guy?

There is this girl, at my school, and we aren’t best friends, but we still talk and hang out. I got over Brock, and I like this guy, his name is Jonathan. We were texting each other earlier, and she asked who I like now that I’m over Brock. I said “Jonathan, why?” All of a sudden she was like, “Don’t text me, Instant message me, call me, or talk to me ever again!” I was kind of freaking out, because I’m like, what did I do?! So I texted her back, and I said, “umm what did I do, what’s wrong?” She sent a duplicate of the last message. So I did the same. When she texted me back again, she said, “your not allowed to like him, I liked him first!!!” So I’m like, “What does that matter..he’s a guy..” She sent a duplicate. I stopped texting her, and I got on AIM. I was telling everyone that happened, and they’re like, just don’t talk to her, she’s jealous because he kind of likes you, he told me. I don’t want to go out with this guy if it’s going to make her mad, but if she’s going to be mean to me why shouldn’t I? If I like a guy, why should I let her stop me??? How can I get her to stop freaking out about this whole situation? Thanks :)