My GF (F25) thinks I (M27) fancied another girl at a party, how do I convince her she's being paranoid?

So last night my GF came to a party I had with a few mates. One of my mates used to date a girl named 'Sarah' from another university. Sarah's really hot and she's a model - not like professional or anything, but she does a fair bit and has been on the cover of a fashion mag. I'd met her once or twice before and she's really friendly and nice, not stuck up at all.<br><br>So at the party, I was talking with Sarah and a few others for a while. My GF wasn't there at the time. She showed up and I went over to her straight away to hug her and give her a kiss and talk to her. She seemed a bit off but I just thought it was because she was tired. I tried to persuade her to stay for at least a little while but she said she was going to head back home, and I went with her.<br><br>On the way back she was asking me who all the girls were that I was talking to, and I honestly didn't even realise she was talking about Sarah at first, but then I said something like 'oh that's Sarah', and she's like 'the model one?' And I said yes. And she just started shouting at me that I fancied her and that I was flirting with her, which I wasn't. She stormed off into her flat and slammed the door on me.<br><br>I don't know what to do. She thinks I was flirting with Sarah, and she's going to keep thinking that. I wasn't, though. How can I prove it to her? She just keeps accusing me of fancying her and that I was flirting with her. It's honestly not even true at all. I'm just friendly to everyone, does that make me a bad person? How can I get her to see that I wasn't doing anything wrong? Or do I just have to let the relationship die?<br><br>EDIT: Thanks guys, I really appreciate all the help. I'll talk to her tomorrow and see what she says. The thing is, she get's like this pretty often. Any time I talk to a girl, she always thinks I fancy that girl. I honestly don't even know how to make her see that I don't, because she just won't listen. She always assumes the worst in me, without even talking about it first. I don't know whether to just end it or keep trying to make it work... Dahell do I know..