I know rehoming is so frowned upon but please hear me out first, this is long sorry.
When we moved into our current house, the previous tenants cat kept coming back because they had only moved around the corner. Everytime we opened the back door it would come into the house, and we'd take it out again and we had to be careful about keeping the back door closed which was a total pain having small children. Some time later the Tennant's came to pick up some post as they often did, and we got talking about the cat and it turns out they'd now moved further away and left the cat because it had gradually stopped coming to them for food and was miserable whenever they caught her from our garden and took her away. She was in great health and not underweight considering she'd been homeless for some time. At this point knowing she didn't have a home, we started to feed her.
We were cautious because DH has an allergy to cats, but we found that he didn't seem to react to her. We did some research and found that black cats are usually less allergenic and often people with cat allergies don't react to them so we thought this was the case. He didn't get the sneezing, steaming eyes and asthma he usually got when we visited others who have cats, so it felt right to start leaving the doors open and letting her in to our house and she soon became our pet.
Fast forward a few years and we are about to move house and it wasn't a question about whether she would come with us because she is our pet now, but we have been worried because she loves to be outside a lot and is so territorial about our yard. She does not tolerate the neighborhood cats at all. Last year a neighbour got a new cat who is very bolshy and tries to run into our house a lot and is constantly roaming into the yard and our cat is so agressive to it and can't tolerate it at all. She was very stressed for a while and losing hair, but after a year this Tom now finally seems to be learning to stay away and she is much happier. The other neighbour has just got a new kitten and started to let it out and it's happening all over again. We know the new house has a feral cat and lots of neighbourhood cats so I've been wondering about how she will cope.
Now here comes the problem. DH has had chronic chest infection for the past couple of years or so that won't go away and gets worse and worse, he has had x-rays, CT, countless blood tests and endless antibiotics and steroids etc etc He doesn't smoke. A lung specialist rang yesterday and said his allergy markers are very high and his blood tests are suggesting he reacts very strongly to cats and if we have one we need to re-home it. Because he hasn't had the usual rhinitis like with other cats we hadn't linked it (he has had sinus infections but randomly) but his asthma did start to get worse when she moved into the house.
So I feel absolutely awful but given we were about to tear her away from the house she is so territorial about anyway and she was going to have to go through some degree of stress, now seems the best time to try and find her a new home. What I wanted advice on, is she reacts so badly to other cats in our yard, I'm assuming it won't be possible for her to be rehomed with people who already have cats? Or is this something that she could get used to? We have cat loving family members that might take her on if we asked and we would much prefer this but from how she reacts to neighbours cats will we need to try and find someone with no other pets?