Hi all. Been lurking for a while but I'm finally desperate enough to ask for help. I'll start with the short version of my story and then dive into the long one: Basically, I brought a near adult cat into my home of three already established cats about a year ago, and she's still a bully. Chases the older one and fights with the younger ones. Long story version: I found Mimi at a shelter in Montana last year when I went down for a trip and wound up falling in love with her (Never go in 'just to pet them'). She wasn't a kitten by any stretch but she was probably a little less than a year old, since she's grown about another third in size. When we brought her home we made the mistake of bringing her straight in in her carrier after a long drive. First interaction with Trixie (The Youngest) seemed okay. Trixie was genuinely interested and approached the carrier with absolutely no hesitation. Mimi hissed and spat and that was the end of that before we took her down to my room. I'm in the basement and have a decent sized bedroom, so she has everything she needs down there with me. Next few weeks we try bringing her up a couple of times, but she chases and terrorizes the others and instead of just letting it settle my mom was extremely worried about Trixie, who would sulk and hide for a day afterwards, and didn't approve of letting her up. So, Mimi stayed in the basement most of the time, but Trixie and Amber (The oldest, about 16) would come downstairs and play paws and be hissy at the door of the bedroom on a regular basis. I should mention that the other cats' litter boxes are down in the basement as well. At this time Mimi was very prone to peeing on the bed or laundry if her litterbox wasn't immaculate and especially if I was out overnight somewhere. There were a lot of days where I had to wash sheets and blankets unexpectedly. She's since become much better about her litter box but can still be fussy, not abnormally so, though. Another interesting thing we've discovered is that she is very obedient and intelligent. If you say 'no' to her about something even once she won't try it again and she fully understands when someone is upset at her. She's also very sensitive to sounds and people holding things. My mom once had to say 'no' to her upstairs when Mimi was thinking about going up on a decorative table, and my mom happened to be holding a rolled up magazine at the time (With no intention of swatting her, just by circumstance) and Mimi looked absolutely terrified. She is a rescue and was found outside in wintertime but besides that we don't know her history. So fast forward a yearish, and we still try to bring Mimi up every day. Our vet recommended we give Mimi a hormone shot which I can't remember the name of, but is basically progesterone and makes her think she's pregnant. It was supposed to calm her down, but no difference. The main behaviour I'm concerned about is her chasing the oldest one and her tendency to corner Trixie and get into an all out brawl. When she chases Amber it's almost like a predator/prey thing, since Amber is very small and quiet and will basically try to run. Mimi chases after her and has cornered her a couple of times, but I've never seen them get into a tangle of fur like she does with Trixie. Usually we use our best judgement in breaking up their tiffs. When it's just hissing and intimidation I'll watch but not intervene, but if I know Mimi's going to try pushing things I'll sometimes call her off. When they do get into full on fights I take her back to the basement without a word. So far she respects Pips (The middle child and somewhat dominant cat) enough to ignore him, jumps on/corners Trixie, and chases Amber. There have been a few times where I can't tell if she's attempting play behaviour or being straight up aggressive. There have been a couple times where it's definitely aggression, but sometimes it just seems like she's bugging them and goading them on. She'll still run up on Pips The middle child if his back's turned, but as soon as he notices he'll holler at her and she backs down. I tried once to hold her in my lap and approach the others, which I know is a huge no-no in cat behaviour world, but she didn't lash out and seemed fairly calm and maybe even a little scared. I didn't restrain her from escaping but she nestled into my elbow while the others hissed and watched her. I should mention that all of our cats are spayed/neutered and that the middle child Pips has so far been able to hold his ground, but usually clears out of the area as soon as Mimi shows up. The relationships between our three cats are quite good. Pips occasionally antagonizes Amber but nothing worrisome, other than that Amber keeps to herself but Pips and Trixie are best friends. All of the previous cats we've gotten have come in as kittens. Our house has a good layout for private areas, which is my one blessing, since the living room/kitchen/dining area has sliding doors that can separate it from the rest. Attached to that same area we have the door to the backyard, which is essentially cat proof and has cat flap access for the others. Usually this is where Trixie and Pips go when Mimi shows up. Amber we try to close up in another bedroom when Mimi has the run of the house. We don't have set feeding times except with wet food. We have a large bowl of dry cat food and water out for all of them at all times, with a very firm dinner time routine for a couple blobs of canned food every day. Mimi does not get wet food as her stomach is weirdly sensitive. If she eats anything besides her dry food, even cat treats, she farts the place up and sometimes gets diarrhea. Overall I know we've done this in an unorganized and stupid way. I feel like if nothing changes I'll have to rehome Mimi which would in all likelihood break my heart into pieces. I've never been this bonded to a cat and she's really a wonderful animal around people. She's so affectionate and I feel terrible having to close her up in my bedroom when we're out since she loves her humans more than anything. None of us expected it to be this bad despite knowing it would be a challenge to get adult cats to get along, especially since Mimi was sharing a space with two other cats when we met her. To add insult to injury she's becoming more and more insistent about going upstairs in the morning when I'm trying to sleep and getting very vocal and antsy. I'm really at my wits end here and I've shed more than a few tears over this, so any advice or stories anyone has would go a long way in helping me. Mostly I'd like to hear if anyone has success with Feliway, since it seems to fit my situation but I'm worried it'll be another flop and Mimi will have to go. I love her more than anything and she's actually like a baby to me, but it's not fair to her or the other cats if it stays like this. Thank you if you read this whole thing and thank you to anyone who can help me out here or offer anything to make me feel like I'm not a terrible catmom.