A huge behaviour problem between two cats

Hello!

I am writing here desperately needing help. I have been an owner of cats all my life. I rescue cats in trouble, from the streets, from bad people, i foster them until they find new homes. My own cats are 2 - Koko and Suzi, they are siblings which i found 7 years ago abandoned in the garbage. Since then i have been taking care of them. They went through all of my rescues and never had any problems with the newcomers. First they ignore the new cat and after time they become friends - classic scenario. Until Sissi came along. When i rescued Sissi i immediately knew she will be my third cat. I was fascinated by her but it took me a long time to admit that i want to keep her for me. So, the problem is between Sissi and my other female cat. Let me say some more details beforehand
Sissi came to me from one of these horrible places where insane people confine numerous cats out of misunderstood mercy. Sissi was living among 23 cats and 9 dogs in a two bedroom appartment. Stench and dirt and diseases surrounded everything. She had behaviour problems even then. She used to bite people, did not want to be touched and was very afraid of everyhting. These things are more or less valid now, as well. She does not like to be touched or caressed. I am okay with that. She comes to me, seeks attention, i see she loves me in her unique manner. The big issue is the aggression she shows towards my other female cat. It is not even aggression, it is more like harassment. Here i must say that from the moment i brought her home, she was aggressive towards ALL cats. I started introducing slowly other cats to her using a glass door. She used to make her nose bleed just because she banged the door with her head in the strive to get to the other cat. Then i used leash and started entering the room with her. Nothing helped. She rushed after both of them like a wild animal.
Then i had to move in a new place. I saw a good opportunity in that because the new place would be no one`s territory. I let the three of them in the new appartment without any leashes or doors and Sisi was not so aggressive any more. So i lived in a relative peace for two years. Not without conflicts but not like before. Now she became again intolerable. The most interesting part is that Sissi is not aggessive towards male cats, only towards my other female. And as a result Suzi (my older cat) is experiencing a lot of stress. She cannot go to the cat toilet because Sissi attacks her immediately. She started peeing on my kitchen towel. She lives now only at the kitchen broad. The moment she is down, she is attacked. Sissi does nothing else but keeping track of where Suzi is located. I do not know what to do anymore.
I must say also that at the moment there are two rescue male cats at home, too. Sissi shows no aggression towards them.
Please, if anybody has any suggestions, i will be very grateful!
I am also searching for a cat behaviour specialist or cat whisperer or some organisation.
I tried everything - scoldinh her, punishing her, ignoring her, loving her more - nothing helps.
I cannot watch my good girl suffering like that.
Please, any advice will be helpful.
Thank you!

I was afraid of such a suggestion. Yes, this might be the case with Sissi. The problem is that i decided to adopt her because she had spent really a lot of time in a rescue centre (which in Bulgaria, believe me, is a lot more different than in other contries) without any chance of adoption. The reason was that she is not like a normal cat with humans, either. She does not want to be touched, let alone petted. She still bites when i pet her more intesely. People here rarely adopt grown cats and the ones that have some pecularities like Sissi do not even stand a chance.
Last year there was this woman who finally wanted to adopt her. We brought her in her home and Sissi behaved like a wounded animal. She did not stop miawoing, walking constantly back and forth, eating nervously and the woman said that this is a torture to both of them. We have her a night there and the woman decided Sissi needs to go back home.
Actually Sissi is very attached to me or at least i think so. I was the first human who treated her well and i think she knows that. So that is why i still think there is a chance i could influence her and make her more tolerable towards other cats. The problem is that i do not know what attitude i should have.

Wow, Otto, thank you so much for all of the advice! All seems very helpful. I will read your post again later more thoroughly.
To answer your questions:

The two newcomers actually are living with me for almost a year now. Reason: one of them has cerebellar hypoplasia which makes adoption harder. The other cat is his playmate, they bonded so well that i decided not to separate them. Now i am searching for a home for both of them together abroad. With God`s help they might soon find their new and hopefully permanent home. They are both male and Sissi sometimes confronts them but not as she behaves towards Suzi (or Susie i think is more correct in english).

Sissi was checked last week by my vet. I did that first. No visible signs of illness. But let me elaborate a little more of her behaviour. When Susie is in the toilet, she waits for her behind the door and jumps over her when she is out. Moreover, she constantly looks for her, follows her movoments in the room and when Susie approaches, Sissi takes a position for attack. I do not know whether i am right but i keep thinking that Susie is actually afraid of Sissi. Unlike her the other cats are not. So, Sissi knows Susie is afraid of her and takes advantage of that. The others are not and Sissi just cannot find anything to be spiteful for. Does this sound logic to you?
For all those years Sissi never started a play with any cat. And i had little kittens who somehow always made their way to older cats` hearts. And Sissi herself is playful. She is active, never afraid of the vaccuum cleaner, just on the contrary - when i start vaccuming, she is lined up before the couch, knowing i will get her mouse from there.
One more thing - Sissi never fully ever accepted the other female. She just had a period of tolerance towards the other girl. But now she is back to deliberately seeking with eyes for the other one and attacking.
So i was thinking of some way to increase confidence in Susie so she can overcome her fear. Is that possible with cats?
Yes, my next step is Feliway. But i read that cats get used to those pheromones and the effect is only temporary. Today after work i will try to buy it.
Here are some photos
The aggressor Sissi


Susie (the first cat from the left) and Sissi when they had tolerance to each other


I have 3 toilets. Maybe i should buy another one.
Vanila - the one for cooking?
This sentence of yours is interesting to me - "Or, you may be dealing with displaced aggression, something has set Sissi off (maybe the new fosters) and she has remembered her antagonism to Suzi."
One of the fosters, the one with the CH lately is seeing himself as some kind of a leader. Yes, he is supposed to be disabled and poor but just on the contrary he is living the time of his life. He is now a teenager which you know what means. I noticed that recently he chases everyone to play with but he does that in a very brutal way, mainly because of his disability. So, do you think that he might have triggered Sissi, who on her part, decided that she had an ally to fight against the other female?
I am sorry for the long post and bad english. Thank you all for reading and helping!
I hope tonight i will have Felliway at home and see if it will work.

Hello to all again!

I ordered Feliway and i am using it for 2 days already. Also, i have contacted a lady that was an animal behaviourist (is that the word) and she prepared me a list of questions. I hope she can help us. So far i do not see any change in neither of the cats. Concerning Feliway - should i unplug it when i open the windows to get air?
I started locking Sissi and the other boys for an hour in the bedroom because Suzi refuses to get down to go to the toilet. I cannot imagine how much stress is that (
I am desperately searching for a home for the two boys. Their wild games and especially the attitude of the one with the disability are making things for Suzi from difficult to unbearable. I am sure of that because for the Easter holidays i took Suzi and her friend Koko to the countryside where we have a small house. The change was more than visible. Suzi played like a kitten and looked very satisfied.
I thought i understood cats. But these few months just made me realize cats are unpredictable. The kitten with the cerebela hypoplasia i always thought was poor and miserable and needing help and sympathy. Now he is the boss of the group. He harasses everyboyd including his friend with whom he grew up. He is jumping over him, biting him on the neck while he screams. I know this is a game but why is he so rough and brutal? When he sees a cat on the floor he immediately rushes to her and chases her. When she climbs up somewhere he starts roaming the room making sounds that suggests he wants to play. And i think this is what provokes Sissi to do the same. When Sissi was living alone with Suzi and me they tolerated each other with fewere conflicts. They were not friends but tolerated and avoided each other. So that is why i think Sissi is provoked.
I know this is an american forum but if you have any friends in Europe that will be willing to adopt two young boys, please forward them my blog. Here is their story - http://catsneedinghomes.wordpress.co...-special-cats/
If they got adopted it will be easier to deal with the conflict between the two ladies.
For the moment i am relying only on Feliway.
Thank you all for reading.