Kitten recovered from FPV, still has severe diarrhea

Hello Vets of Reddit! Thank you in advance.

We are currently seeing a veterinarian, but I would like a second opinion. Located in Southern California.

My kitten (Freya) is a spayed female domestic shorthair, approximately 10 weeks old. We are not 100% sure of age because I am pretty confident that the shelter lied about her age. I would say somewhere between 9 and 11 weeks. When we brought her home, she was having diarrhea. The shelter told us that this was due to a new treat that she was give

n at an adoption event, and that it would clear up. They sent us home with pro-pectalin.
A few days later, I took her in to the vet because the diarrhea was not clearing up, and I was noticing some possible ataxia. He immediately clocked the ataxia, anorexia, and inflamed anus. He tested her for FPV and the result was positive. They gave her SC fluids, metronidazole, zofran, an appetite stimulant, and prescription wet food, then pretty much warned me to prepare for her to die. This was three weeks ago. I am so happy to report that she survived and has since tested negative for FPV (and a fecal sample came back negative for ova and parasites) and all neurological symptoms have subsided. She has still been having diarrhea consistently, but it was starting to firm up and we were feeling hopeful.

The reason I am writing is because the diarrhea is getting bad again. I called the vet and he prescribed another round of metronidazole. This honestly seems to be making things worse. She is having trouble controlling her bowels, I don't know if it is involuntary or if she is choosing to go everywhere in protest. After some research, I disagree with the choice to prescribe metronidazole (for many reasons), but I can't seem to find any other suggested treatment. I plan on asking the vet about a probiotic to add to her diet. Maybe a different food? Right now she is eating Purina ProPlan EN Gastroenteric wet food (~159 calories/day, spread out), and I am supplementing that with a small scoop of Hill's Sciene Diet kitten food (~70 calories) since that is what the shelter provided.

Any and all thoughts would be so appreciated. Thank you.