Oh our trainer did tell us that the stay command can be hard to teach a young puppy so she usually waits until they get a little older. No idea if this is true but I know trying to teach Geno to stay when he was that age was really rough, but that's cause he's a hyper little guy. Probably depends on the temperment of the dog too at that age. Good luck!
She sounds like a really smart puppy though so hopefully you don't have any trouble!