It is very dangerous, if not deadly, for a 3 lb yorkie to have puppies. Before I had Yorkies I never knew that, I had no reason to know. Not trying to scare you, but you should just be informed of that since you had mentioned you would like her to have puppies some day
. Typically, when dogs breed, they will be tied together for a little while. That does not mean that your dog did not tie, because she could have tied for a short time, but it is good that you did not find her stuck to another dog. Is there anyway you could find out who's dogs those were? You could find out if they were male or female that way.
My Lilly just had her 2nd heat and sometimes it's hard to notice with those little dogs and all that hair
Especially if they are not acting any different or cleaning themselves a lot.