I feel horrible to even ask..

okay.. so I'm probably the worst aunt ever.. But I just need to know if anyone else feels the same way. Okay so here's the story. I announced I was pregnant with my daughter and a few weeks later my sister in law announced she was pregnant. We end up having the same due date. Going through our pregnancies she was always more sick, more uncomfortable, just milking it through her whole pregnancy even though I was the one hospitalised twice during mine and ended up having my daughter a month early. But anyways since the day she knew I was pregnant my SIL has treated our pregnancies and daughters milestones and such as a competition. my niece and daughter are now two years old. and I really don't feel that bond or love for my niece that I have and feel so my other nieces and nephews. I don't know if this is because of the way her mom is always acting or if its because she's always being a bully towards my daughter. she's always hitting and screaming at her and her mom does nothing. But I really don't like having my daughter or myself be any where near my niece because I feel like I always have to be between the two of them to keep my daughter safe. I don't like feeling like a bad aunt but my daughter comes first no matter what. has anyone felt the same way as I'm feeling? any tips on how to make the relationship better? please help!