So sorry for your loss. My moms rescue yorkie passed of the same thing. It is all about genetics and good breeding. Yes the smaller ones can get injured more easily but that’s avoidable if you’re careful. Just an added note just because they are AKC breeders doesn’t mean they are good so make sure you look into everything. Like not breeding females under 5 pounds, they do all the OFA test available (
https://ofa.org/chic-programs/browse-by-breed/?breed=YT) that the dogs are raised in the house, they keep the puppies until 12 weeks and so on.