First of all, my policy with my own puppies is that each family has 72 hours to have the puppy examined by their vet and have a full fecal panel done to confirm that they received the puppy in the condition I state it is in. This is WAY more for me than for them because it means that after that check up they can't come back on me for anything that shows up after that - mainly meaning worms or something picked up in their new environment. I also don't want them coming back and saying the dog had a broken leg, or scabs or something. My vet sees all my puppies within 3-5 days of them leaving me so I KNOW they are healthy and sound. I also run a full fecal panel (smear, floatation, and Giardia Anitgen test) on every litter (if one puppy has worms or Giardia or Coccidia they ALL will). Again, peace of mind.
After 2 weeks, unless the lady is saying she saw bloody, mucosy stools from the 1st or 2nd day home, I wouldn't have paid for anything. Yeast infections also don't just show up after 2 weeks. Hasn't she taken the dog to the vet in between there? Had it examined? This is important with any new pet - just for the vet to get acquainted with the dog and what is normal for them.
I would offer her a full refund and take the dog back. Tell her she's obviously not happy with it and you pride yourself in your families being happy with their new additions. My contract very clearly states I don't pay vet bills. I will make an exception if something shows up on that 72 hour check up. If it's an inherited problem and requires treatment that exceeds the cost of the dog then I offer a full refund once treatment is complete.
Parasites are tricky to pin down where they came from. Have you run a Giardia test on one of your own dogs to rule out that you exposed the puppy? I would doubt you did as it would have shown up faster if you had a case - especially in puppies. Cleanliness is not so much the issue with Giardia. You can walk your dogs, step in feces that is infected, one of your dogs licks your shoe and they have been exposed. When breeding it's important that you periodically run fecals on your own dogs to avoid puppy exposure - but your best bet is using a good wormer and running fecals on the puppies at 6-7 weeks to rule out parasites.
But knowing you - I would put money on the fact that the lady exposed the puppy herself.
"I would offer her a full refund and take the dog back. Tell her she's obviously not happy with it and you pride yourself in your families being happy with their new additions." - Abbylynne
I totally agree with "Abbylynne"! With all "due respect" to the woman who purchased your puppy, she sounds like either a fruitcake or a weasel & I know you won't rest easy, either, having one of your puppies in her home. Please do keep us posted. My fingers are firmly crossed you get your puppy back & can place it into a loving home, the key word here being "loving" - :-)