I definately would not breed her the first time she goes into heat. A minimum of 2 years old or at least their second heat is recommended. My advice right now would be do not breed your dog, get her spayed.
If you are really interested in breeding, then take this next year to do
a lot of research. Have your girl evaluated for the Yorkie standard by a couple of experienced breeders who have shown their dogs. Evaluate her physical attributes for carrying puppies along with thorough testing for genetic and communicable disease by the vet. Read all you can about breeding toy dogs. Understand that it is always a risk even if your girl is over 5 pounds and in excellent health.
Then IF your girl is really breeding material, be very careful about choosing a mate. The sire should compliment her -- for instance, if she is within standard but has ears that are a little on the large side, find a male with small ears; if she is a little short legged, find a male that has a more square measurement overall, height being equal to length). Make sure the male has also been genetically screened and is in good health.
Do not breed just because there are a couple of cute dogs and one is in heat. It is just not worth it and you may be very sorry in the long run.
Here are a few links to read -- all with titles like "Should I Breed My Dog" :
Breeding Your Dog To Breed or Not To Breed, Should I breed my dog? Should I Breed My Dog?