She is so cute! If I were you, I would get the blood test done. Being afraid and not knowing will only make you stressed out which isn't good for your puppy. If it is thyroid, the vet can start her on a supplement which is very inexpensive. The breeder was upfront with you, and I think there is the possibly she could be a dwarf. But that doesn't mean she can't have a normal life. I would follow through on the tests, take your vet's advice, and enjoy your puppy.
Sting Chance von Gaard AKC GSD 2/8/2006