I've not ever talked to the vet about the sneezing because it never manifests at any other time than play....specifically 'play biting' (when they're wrestling). She doesn't sneeze when she's running or otherwise playing. It's the oddest thing!
So yours sneezes when she lies on her back!
I love how Yorkies tend to sleep on their back. Talk about adorable! I hope your little one finds a comfy way to sleep sans the sneezes!