When I was married, my wasband & I mutually agreed that each other came first. We were a team. We were also very far removed from both families physically so we HAD to depend on each other. I was fortunate that my family was respectful of boundaries. His overbearing mother was problematic at first (she rearranged my cupboards the first time she visited our home because "her way was better") and he put her in her place by saying I was his chosen family. There were a few times that family took priority, like during times of illness/crisis. It was far more likely that HIS family was priority over mine, but at the time, I viewed them as my family so it was fine. It was rare that mine was the issue, but it did on occasion, but he viewed my family as his own, so again, there was no issue. We were in alignment on these so all was good.
He had a friend who always seemed to be a higher priority than me, though. This friend was a total flake, took advantage of his friendship (back before unlimited cell phones, this friend ran up a $2k bill on my phone and chose not to pay us because "he couldn't afford it" even though he lived with us FOR FREE, never paid for anything, etc.) and was frequently a source of arguments because I didn't like how selfish and self-centered he is. I had more of a problem with his friend than his family... mostly because he would not "correct" his best friend. We were NOT aligned on these so it was an issue.
If you hope for success in your relationship, you need to learn how to communicate your needs in a way that is not perceived (by her) as complaining or threatening. You need to learn how to be heard. You need to be a team.
Best of luck.