No, a parvo test is generally not a part of a health certificate. These certificates certify that an USDA accredited veterinarian has examined the dog and finds no evidence of contagious disease. It is impossible to run specific tests for every virus that a dog could carry before issuing one of these certificates. Even if we picked the ten most common viruses, it would push the cost of a health certificate to over $500 per puppy.
The liability question is one for a lawyer. Certainly, the exposure happened before you got the puppy. I would think you would need to demonstrate some negligence on the part of the breeder (i.e. improper vaccination of dam or pups, known and undisclosed exposure to the virus, etc.). As long as the puppy appeared healthy when the health certificate was issued, I believe the veterinarian has no liability. Some breeders have a health guarantee in the purchase contract. That would be the easiest way to try to recoup some expenses.
I'm glad to hear she is on the road to full recovery!
This post provides general information only and should not be used to diagnose specific patients. All treatment decisions should be made in conjunction with a veterinarian after thorough examination.