Bfs niece...

So my bf had a niece the same age as me we actually use to be friends but when I started seeing her uncle who's only 5 years older than use, she instantly hated me. And has ever since even three years later, and we've had a rocky relationship in the brining so in a way I understand but were way past from what we use to be and we live together now. Well tonight our best friends (who are dating and have been before we met) well she left him tonight pretty much and my bfs niece came over to swim and be my was telling her about it and made the comment "oh it'll probably be 8 hours before they get back together" and she replied "sounds familiar" I knew she was talking about us and our past(as she gave me a dirty look). It pissed me off and I left to go talk to my best friend for a bit. It just sucks she still can't accept mine and her uncles relationship because I feel like it puts him I the middle, and I'd have no problem but she always makes the problem with me. And it made me really upset I can't even be at my own home because she comes over and has to act like that, when I don't say a word or try to be nice. She's not going to end our relationship whatsoever but it's an issuse to. There's almost nothing to do but it's hard.