New Friendly Cat Aggression Towards Existing Cats

Hello, friends! 

I recently saved a very dehydrated malnourished 1 year-old cat off the street, got her shots and brought her home. We immediately kept her safe and comfortable in our small second room. It was an uphill battle as she wasn't comfortable being touched, although she loved being near people. Over the course of two weeks she became very loving and became comfortable  with receiving attention and even began to play. However, she became very aggressive when laying eyes on my two other cats. I began following instruction I found online on how to integrate our cats very slowly. I have been feeding them closer and closer to one another every meal. It's now been 1 month and she is just as aggressive towards the cats as she's ever been. 

I would be comfortable being more patient, the only problem is that she's very tired of being cooped up in that small room. She cries all night, because she is lonely and desperately wants to be out of the room and hanging out with myself and my husband. The moment someone goes into her room, she stops crying. She picks and pulls at the door for hours trying to get out and it's very sad to think that she's so unhappy in there. Our apartment is only a 1 bedroom and there isn't anywhere else we can keep her away from my other two cats.

Does anyone have any advice on how to make this integration process more comfortable or more smooth for her? Have you found any techniques to ease cat aggression? This cat is so loving, I just can't understand why she's so angry toward my other two very innocent, sweet loving cats!

Introductions can take months and months and months.  I brought a feral/stray into my home 2 years ago.  He too had a room of his own. It took one solid year for he and my resident cat to learn to coexist.   I followed the guidelines of introductions after he had been in the house for 2 months.  I first wanted him used to humans and touch.  I had another cat and also a large dog.  I thought all was going well, but I rushed the process.  You don't want to move on to the next step until all signs of aggression are gone.  When you try to feed them near each other or behind a door and there is aggression, you are not ready to move.  Try feeding on either side of a closed door and get the bowls as close to the door as possible.  If you hear growling or hissing or someone won't eat, move the bowls back.  You can then progress to using a baby gate in the door.  First cover it with a sheet and gradually move it up.  This could take weeks and longer.  I also used a cheap screen door from Lowes.  It was wooden and only $20.  I attached it to the door way with tension rods so I didn't have to deface the door.  It allowed the cat in the room to have more a feeling about being a part of the house.  I kept a baby gate in the door way for extra protection.  I only did this when I was home to supervise as the screen was a bit flimsy.  I have pictures of the setup if you'd like to see.

Also you need to allow the new cat time out and about in the home.  Put the other cats away for awhile.  This will help things as the new cats scent will now start to mix in the house.  Just make sure all are safe.

Have you tried feliway plugins.  You may need a few of them.  Composure liquid max is a nonsedating calming supplement that can help with aggression.  I used it on the cat I brought in.  He was very territorial aggressive.  I mixed 1/2 t into his morning wet food and 1/4 t. into his night time food.  You can find it on Amazon.

As far as the crying at night, I am sure she wants out.  Yet for safety purposes she needs to remain safely in her room.  You can try putting the other cats away, but that may create issues as well.

Lastly, has this new cat been to the vet for a check up and to be sure she is spayed?  You don't want her interacting with your other cats until she has a clean bill of health.  Also she should be spayed or you will be dealing with lots of yowling and behavior issues when she goes into heat.

Thank you so much for all of your advice. We have had a baby gate in her doorway for her entire stay in our home. Which has been very good until she figured out how to jump over it and even slip through the bars (she's pretty small). I  would love to see your setup of the screen door w/the baby gate! That sounds like it might work for us. 

She will eat just across the baby gate with our other cats just fine. As soon as she sees or hears them when it isn't feeding time, she freaks out! 

I have installed the feliway diffuser in her room as well as spraying some of the jackson Galaxy Spirit Essences products in her room, on her food, and on her fur. I haven't tried composure liquid max yet though, I'll try that!

She also has been completely checked, given her shots, and spayed by a vet and is in 100% perfect health. So, none of this is a health issue. Good question, though.

I am wondering where she learned such intense aggression from as she's only 1 year old! I'm hoping her mind is young and we can shape her into less aggressive habits.

Thanks again, please send along those photos for me!

The aggression she learned at such a young age is most likely a survival mechanism.  She had to be on alert at all times and fight off predators and enemies.  She will adjust to a loving home, but give it lots and lots of time.  The feral/stray I rescued took a long time to adjust.  He has been inside for almost 2 1/2 years now.  He is still skittish when people come over ( no one would ever know he lives here!), he hides when we vacuum and loud noises still startle him.  Yet he now loves our other cat, sleeps in our bed most nights and is so sweet.  Yet the scars he has from living on his own run deep. 

Here are a few pictures of my set up.  The screen on the door is pretty flimsy, thus the need for keeping the baby gate in the door way.  It was a bit of a pain to put up and take down, but my DH didn't want to attach a screen door and mess up the door jams.  This worked well for us.  I never left home with this set up.  I didn't quite trust the set up, but when we were home, it was great.