I had 2 dogs that had pyometra @ the age of 6 months. One was a Great Dane and the other a German Shepherd. I know that you have to be very careful with anesthesia on little ones usually under 2 pounds. If your dog is in good health it should be fine to put under. Check with you're vet. As far as not having as long a lifespan as a larger Yorkie I would check with your vet. And the reason to spay is if your 3 pounder were to get pregnant you could possibly lose her and the puppies! That would be tragic...