my bfs niece doesn't like me for some reason.. She's 12 and I've been dating him for over a year and…

my bfs niece doesn't like me for some reason.. She's 12 and I've been dating him for over a year and we're having a baby soon. I get that he's her favorite... But she always gives me cold hellos and goodbyes sometimes nothing at all .. well today I said hello and I tried to start a conversation and she just looked at me like I was stupid. And kept walking and when I went to my BF i just burst into tears I tried to walk away before he saw me but it was too late lol my pregnancy hormones got the best of me :( I don't know why I cried I was bothered by her attitude but didn't expect to cry .. He said he'll talk to her because it's ridiculous how she acts towards me when I do nothing to her but omg can't believe I let a little girl make me cry lol