The problem is that she probably signed some paperwork when she got the puppy. Lots of pet stores and large scale breeders have some kind of legal protection against things like this. When you sell lots and lots of puppies, there is bound to be one that has something drastically wrong with it. Usually you'll have to sign off on something kind of like a warranty. Most will say something like, after 15 days its your expense to take care of the animal or after 1 year if a hereditary issue hasn't appeared, it is then on you. Some places will pay up to the price of the puppy for vet bills if you don't want to return/exchange it for another puppy. It varies depending on the place really.
I think it will be unlikely that much will result legally from this. Maybe the "breeder" will be inspected by animal control more regularly making their lives more difficult or maybe they'll incur some fines as a result, but I'm betting they've covered their rear ends in some way unless they're BRAND new to the business.