She did it!

 Mercy's lab results are normal. She has no parasites or bugs that can affect appetite or defecation. The vet listened, asked a couple of questions and then urged patience and persistence because all of Mercy's responses are fear-based and stem from her earliest days as small kitten alone. The vet said she might offer Mercy medication for anxiety but at this stage, just introducing things gradually is the best course. She is frightened of  the unfamiliar, so I'll go at her pace and praise her for any milestone, hoping that she understands that there is no danger lurking in our home. She is behaving normally and affectionately. The issue is getting her going at a better rate and keeping her hydrated so she can go. The Forti-flora probiotic that she refused mixed in food is acceptable on my finger as I found out this evening. Mercy often licks my hand and fingers as a sign of grooming or affection, so I tried a bit of the fine grain and after three dips, it vanished sans drama or any refusal. She got praise and a treat that she investigated thoroughly before crunching happily. She also used the box and is carefully observing my typing. I'm not sure if it is going to last, but I'll take this as a good result.

A very kind reader suggested baby food as another possibility for added hydration and the vet concurred, so thanks for sharing that tip and your experience. I'll be giving it a try.

Have a good night.