Am i wrong?

Some backstory: my girlfriend lives in a different country and so does my sister so they’ve met once but we’re around each other for 2 weeks but we never did anything together because my gf doesn’t really like her for some reason. my girlfriends brother has a girlfriend too and I’ve met her a couple times. I don’t really like his girlfriend because of her personality and we just don’t click but I’m always nice to her and would never be rude. Me, my gf, her brother and his gf are going to a concert next year because we all like the same band.

Ok so the problem is that my gf’s brothers gf messaged me one day on Instagram saying “can I have your snapchat?” And I found it a bit weird because we don’t know each other and have pretty much jut said hello and bye to each other every time we see each other which was 2 times. She was following me on insta before my gf which also was a bit weird to me. So I mentioned this to my gf and all of a sudden she gets defensive and says things like “why don’t you try to get along with her” and stuff like that when I’m always nice but we just don’t get along for personality rwasons. And so anyway I say that she’s not really tried with my siblings let alone their partners who she’s met. She then says that it’s more important for me to get to know her brothers gf than it is for her to get to know my sister? I don’t agree at all because she met this girl 5 months ago and my sister is my sister.

I don’t know what to do because I don’t want to feel like I’m making effort with people who aren’t even related to her when she doesn’t make effort with one of the closest people to me.

Am i wrong in thinking this and should I just accept it or what?

As well as this my gf keeps telling me things that her brothers gf does for him and makes it sound like I don’t do enough nice things or what i do isn’t good enough and it just makes me like her less because it’s like she’s better and above me