I have a survivor from FP with me. It was really a hard and sad time to watch her handle the pain and suffer badly from the sickness. I lost few during that time and managed to have her alive.
Sometimes, we overlook why cats wont eat. Most of the time it might be their appetite, but sometimes do try to open up their mouth and see whether there are blisters on their gums and tongue. Mine did, and being aware made me the happiest man alive.
And I do hate FP, FIP or FIV. There are so hard to identify yet so lethal and unforgiving.