This really strange girl is being, well, strange :/ ?

Ok so me and my ex boyfriend broke up ages ago, about 2 and a half to three years now, and I have now got a new boyfriend. But my ex boyfriend has now got back together with the girl he was dating before me ( i know its a tad confusing) and now she's acting really bitchy towards me and I don't know why? I have never liked this girl she's an annoying spoilt brat, who has a six-pack and man smile and wonky eyes, and she has never liked me. Me and my ex boyfriend are still friends, he is a genuinely nice guy, and he has asked her to stop being mean before, but why is this girl who I have hardly met before being so weird?