I have a tea cup yorkie when can I mate her
no sooner than 2 years old, but make sure if you do, its another teacup yorkie and not bigger than her and that still wont guarentee she wont have complications or need a C section...small breeds have more complications then larger breeds. If you do breed her be prepared for any emergency to happen and have a vet on call 24/7 if you need it and also the $$ saved up for any vet care she and the pups may need.
My vet told me that it is very unhealthy to breed dogs period, but absolutely not before 2 years old, I've heard of breeders doing it right after the second heat cycle but according to the vet, that puts you dog and her pups at great risk. The dog may not be mature enough to care for the puppies once they are born.