Donna whether you are part of it or not, she probably is going to get a cat regardless if her heart is set on it, it is whether you help her or not is the question, you just have to go with your instincts in this case I feel, probably a FIV pos. cat would not be her best option if there are going to be vet bills ongoing,and even though fostering is an excellent idea, not everyone is cut out for that.
Again just go with your inner feelings on this one, good luck, it is a tricky one for sure.