Hi Theresa M:
Sounds like you’re on top of the care for your dog as you wrote you are “doing what the Vet says.”
My Vet recommends pumpkin for my cats and dog. It worked wonders for my cat a few years ago that was on his death bed from a life threatening reaction to a med. He was not eating and dehydrated. Euthanizing was discussed, pumpkin worked for him!
However, I wouldn’t fool around trying out too many things to remedy diarrhea especially with her condition. Dehydration happens before you know it. If an OTC remedy doesn’t work quickly I would have a back up plan in place with my Vet.
I have never used Firm up, but I think several regulars on DFA have. Maybe they will read this and post their experiences. Some other things I have used to firm things up are apple sauce and sweet potatoes.
Hoping the best for you and Lucy.
