If she is registered, I would at least start by reporting this breeder to the AKC or whatever she's registered with, we don't need breeders like this to be allowed to register more animals this way, they may get suspended. You may have to get a report made from you vet to report this legitamately. Next, just find out if she is pregers, then go from there, and discuss it w/ your vet. If Thom is that much larger it
will probably be a problem, which you should never breed them together if they are that different in size, it would be too dangerous. I would deffinitely report this person, they obviously have no respectable practices going on over there.
I imagine if you can't tell the difference between a 6 month old dog and a 2 or 3 years old dog then you don't know enough about Yorkies to be breeding at this time, Don't mean to sound rude, but that's what I think.