Lizzie,
Even though she came from a large room no kill shelter I still believe she is better off with you than at the shelter. I have two FIV+ cats that live with a friend due to the fact that I have alot of special needs cats in my one bedroom condo that get sick alot so trying to bring them into my already crowded condo is not a possiblity. At my friend's they stay in his bedroom and are perfectly happy and content to be there. Do I wish I had a bigger place where they could live with me, yes but I am doing the best I can in the situation. Ivy and Scooter have a good and safe home and are happy and loved. That is what you are giving Faline. I do have one suggestion for you. I don't know if your vet had mentioned immune boosters or not but there is an injection, I believe the medicine is spelled egstim( some vets use interferon) that Ivy started off getting once a month, now he gets it every two weeks. This is a medicine that is suppose to boost their immune system. recently my vet also added to their regime a lysine paste that they get that is also to help their immune system. If they aren't already on something like this maybe you could ask your vet about it. Ivy I trapped back in 1999 and the vet estimated his age around three at that time. he is doing very well. Scooter I have had about a year I guess and he is about 5 and also is doing well. So please don't feel bad about taking Faline out of the shelter and giving her the love she deserves. Remember since her immune sytem is bad that it will take longer for her to get over stuff. She just needs a little more time that is all.
Melissa