If you have a written contract, you need to read what it says. But, it sounds to me like this breeder knew that the puppy had problems, if the pups had been outside, and at 15 weeks, surely she noticed something-allergies didn't just happen on the way to your home. I am not a breeder, but whenever I got a pup, I have always spoken to the breeder's veterinarian before getting a pup-to find out if any KNOWN problems and to make sure they HAD BEEN to a Vet!. Someone here will be able to give you advice better than I, but I would definitely call the breeder(though it sounds to me like they are dishonest?) It also sounds like you will have a long road ahead -as your health guarantee may not include things that are "common" to some EB's.