Here are some MAJOR red flags when you look at a breeder contract or "health guarantee."
1) The health warranty (which is what it should be called; nobody can "guarantee" health) runs out before the disease would show up. This is SUPER COMMON. People will offer a one-year warranty when OFA won't even certify hips before two years old. Other diseases (most heart problems, for example) won't show symptoms until the dog is fully mature. By making the deadline while the dog is still effectively a puppy, this breeder will very rarely have anybody complaining.
2) Forcing you to return the dog before you can get a replacement. This almost always stops any claims in their tracks - nobody wants to return a beloved dog, no matter how ill. Good contracts replace or refund your dog and do NOT ask you to return him or her.
3) Not knowing the difference between congenital, genetic, and inherited. Congenital means "present since birth." In other words, aside from injuries, illnesses, and toxic exposures, EVERY problem is congenital.
Genetic means that the dog's genes coded for the disease. Since all diseases - and even many illnesses and responses to injuries - are mediated by genes, EVERYTHING is genetic.
What you should be protected for in a warranty is INHERITED disease. In other words, stuff that represents a true oops by the breeder.
Ask your breeder exactly what problems will be covered. Ask them for examples of what is NOT covered. If they can't clearly spell out the difference, run away.
4) She's used words that don't mean anything. Lots of bad breeders will put a line in a contract about "female shall not be overbred" ("overbred" means nothing) or says that the dog should be seen by an "AKC veterinarian" (no such thing - though hilarious! I wonder what my vet would say if I asked to see her pedigree).
5) You are not forced to return the dog to the breeder if you can't keep it. Beware of lines that ask you to promise to find a good home for the dog or similar. The dog should go back to her, no questions asked, no requirements (I once saw one that said they would not take the dog back if it had been spayed, another that said they would not take the dog back if it was not current on vaccinations).
If the proverbial dog poop hits the fan, your contract is what you rely on to make sure that this dog has a happy ending or that you don't end up with a sad story and nothing else. INSIST that the contract be real, useful, and indicative of a breeder who really knows her stuff.