Is your mother in law's cat her own cat or a stray? Cats normally only get FIV from deep bite wounds, or if the birth mother was FIV+ and they end up with it as carriers or develop symptoms. If your mother in law's cat is an only cat, and is fed a healthy diet, and given proper medical attention if she ever gets ill, she can live a long and healthy life. I have a 11+ yr old FIV kitty with me, and another one I fostered lived to be almost 15yrs.

If she's not aggressive, or noth with aggressive cats, she should be fine and wouldn't have to lose her home.

Another question is, if she's had her for some time, how was she exposed to the virus? Does she have other cats, and if so, do they fight? If they do, has she had them tested for FIV, because if the girl was negative before, then that would leave open the possibility that one of the others has it.

Let me know how things go, and what your mother in law decides. If she still wants to "get rid" of the kitty because of her virus , I might have some suggestions for you on rehoming her.