Sick puppy...can i get my money back?

I bought a puppy from a lady with a signed receipt from her stating that i had a 3 month money back gaurantee against hereditary defects or illness. After about 2 months i noticed the puppy's legs were shakey at the ankles so i emailed her to let her know i would be taking the dog to a vet to check out the situation. I had my other dog at the vet & asked the vet (without him seeing the puppy) what he thought it may be. He said he hadnt heard of it before and so he said i should just take her straight to an orthopedic vet instead of bringing her to him. My financial situation prevented me from taking the dog to the specialist right away. I then took the dog to my dads and asked him to help me with the vet bills and he agreed to. It came to $500. It was after the 3 month guarantee was up when the dog went to the orthopedic vet and he told me it was a hereditary problem. The woman i got her from is now saying that its past the 3 months & she "legally" doesnt have to do anything about it because the dog didnt see the vet till after the 3 month deadline. I did however notify her of the problem before the 3 months were up. I have all emails & corespondance with her doented and the written reciept from her. Do i have a case against her to get my money back, and/ or the vet bills paid for? I am not going to give her the dog back though. The receipt doesnt state anything about giving the dog back and she couldnt care for it anyways.. it may need $2500 worth of surgery to fix the problem.Thanks