Yikes! Sorry to hear about kitty, that was a really fast decline that I usually only see with Panleuk infections. Its not unusual to not even know they are sick at that age and find them expired in the morning (without actually showing any symptoms). I really wouldn't be so quick to blame your fostering skills, it is likely that this would have been a no win situation. As gpm points out we will never save them all but taking the time to care does make a difference to their passing, so please do continue to care and foster!