Preventing Disease in Current Pets when Getting Foster Pets

Also...what would you all recommend doing as preventative when looking to get foster cats? I have one cat now, and I don't want to expose her to a new and possibly sick cat if there's something I can do for her to prevent many of the diseases before bringing a new cat in. I have asked my vet but received no response. (Perhaps because the usual $90.00+ office fee isn't attached to it). 

She has all her regular shots, but I am concerned about the respiratory diseases and the "really bad stuff" like FIP. 

Thanks!

I would not expose any resident cats to foster cats at all if it was a short term commitment (less than 4 months). Introductions between cats should be done slowly and carefully so there may not be enough time to make it worthwhile.

For long term fostering situations, I would make sure the fosters test negative for the common diseases and are healthy before any introductions are started.