I (24F) live in a 2 family home that I share with my immediate family. My sister and her girlfriend (both 26F) live upstairs (3bed, 1bath) with our dad, while I share the downstairs (2bed, 1bath) with our mom.

Recently, my sister moved her friend A (26ishF) into the guest room upstairs along with her cat after A escaped a bad relationship.

Our mother has been in Arizona tending to her very elderly father for about 6 months now, so I live alone downstairs. Mom is a bit of a hoarder and while she’s in AZ I’ve been slowly clearing out the apartment to make it functional again.

I’ve spend many hours and a fair bit of my own money to accomplish this. Due to A and her cat moving in, upstairs now has 4 people and 4 animals (3 cats belong to A and my sister, and dad’s dog).

This past weekend my sister approached me about swapping apartments for an undetermined amount of time, which I (stupidly and a little bit stunned) agreed to initially. I eventually retracted my agreement and decided I didn’t want to swap.

There would be a lot of moving around and and my sister’s girlfriend (N) and mom don’t get along due to mom’s generally shitty parenting in my sister and i’s childhood and N being kind of awful. After some snarky back and forth between my sister and I typical of our not great relationship, I pointed out it was a bit unfair that my sister moved in two of the people and three of the animals and is now complaining it’s cramped and trying to move into mom and I’s apartment despite all the work I’ve put in.

My sister is still kind of mad at me, and I feel a little bad because it probably is feeling kind of cramped. Now I’m wondering if me refusing to move is worth the conflict. AITA?

EDIT: This wasn’t really clear from the OG post but she would want to move the cats, her friend, and gf downstairs. One of the bedrooms is locked and fully occupied by mom’s stuff. There is a dining room that used to be mom’s main hoarding spot that I’ve since mostly cleared out that I guess she would turn into her and gf’s bedroom?