I don't like any of the advice you are getting. It is true if she has parvo, her only hope is prompt IV treatment. However, if she had the diarrhea before going to the first vet, he should have recognized the distinct smell. I would go to
Canine Parvovirus, What you should know about for reliable information on parvo. A playful puppy with no blood in its stools, likely doesn't have parvo. It is possible she developed parvo after the first vet visit.
I never had any problem with my new Lab puppies eating, but some puppies take a day or 2 to adjust to their new home. The worst thing to do is tempt a non eater with rich food, see
https://www.askmehelpdesk.com/dogs/i...tml#post254171 Often a sudden change of diet and water leads to digestive upsets.
While you are at the sticky, check out the sections on Housebreaking and ''What does a puppy need?''.