I am sorry to hear you are worried about Maddy. I am a veterinarian and will do my best to help.
When you say her biopsy showed mild disease, what disease was it? Inflammatory bowel disease?
Sorry, bad with abbreviations. I know what GI is, but what is PO?
Dog can go longer than people without eating. Our blood sugar drops after an overnight fast; you have to fast a dog for days to get the blood sugar to drop below normal. I know dogs that will turn down their regular food for days, holding out for table food and treats. Still, I don't want her to go more than 12 to 24 hours without eating.
Sometimes a rest is good for the digestive tract; one treatment for diarrhea is a 24 hours clear fluids only fast.
If she is not eating
to get you to give her something better, I would try not to give in. However, one concern is that she turned down food because she feels sick again. I would monitor her hydration, drinking, and I hope she continues to have nice formed stool.
Let me know what other questions you have.