I have 2 male cats, neutered, very calm and friendly, never heard a hiss or growl, ever. 2-3 months ago, I took in a pregnant female because she was a stray. She raised kittens, they all gone, I got her spayed. I am trying very hard to rehome her, I don't want her, I was just giving her and her babies a temporary home. The whole time, I kept my male cats separate from mother and babies. Now that babies gone and mother spayed, I am trying to introduce them. I feel bad locking my male cats in my room, so I'm hoping the 3 will get along and share my apartment. The GIRL cat is mean! She keeps bullying my male cats, chasing after them, scaring them. Seems like she wants to claim the whole apartment. She invades their litter box (everyone has their own box + 1 extra) and poops and pees in their box, like marking her territory because she doesn't bury her poop. She sits in the boys spaces. I always see the boys huddled in 1 corner together while girl cat claims all territory. I have tried slow introduction, about 30 min supervised interaction a day...the minute she gets aggressive, I separate. Everyone has their own food and water bowl, but she seems to want to invade their food, even though her bowl is full! I am now separating them with a screen door so they see, hear, and smell each other but are not in direct contact. The boys are obviously stressed, not eating, vomiting, scared to use litter box. What do I do? This has been almost a month of slow introduction 30-60 min a day. Boys now hissing, growling...I'm rehoming her, I was just hoping for peace until she goes. Also, she seems lonely, that's also why I wanted to introduce them so she can have friends and play together.