Rehoming assessment - how do you know when it's right?

My family had 4 pets, and we all loved them but only I took care of them in the home. We all agreed to divvy them up, with one family member taking one, I take two, and my main family keeps one. This was due to me moving out and needing to move into a 2 pet policy.

I moved and would visit and noticed neglect. They couldn't clean her litter, feed her, water her, so I agreed to come and do it. But when they couldn't even fill her water bowl, I mentioned it. My family got mad and said to either take her or they would let her out. I obviously took her, but I am already at max capacity.

On top of this, she hates other cats. She was fine in my big family home with space of her own, it was cat paradise. Now she is upset, not many places to hide, and generally uunhappy.

Back at the old home, we tried different methods to help her - anti anxiety medication, scent boosters, calming collars, but she only ever enjoyed her own space.

I feel I need to rehome her, and I'm a foster with a shelter so I could ask, but I feel terribly guilty. Would this be the right choice or do I keep trying to help her? I really don't know what else to do for her.

Not seeking medical advice - she just had her shots and checkup, all was normal.