[C C Kent]

I wouldn't make the decision until the litter is here. Since you are going to do all of the work, you should allow yourself the "pick of the litter." You might even want to have someone with experience help you pick which one to keep, after all you're making a decision you'll live with for 12-15 years. When two Yorkies, or other breeds for that matter, don't get along it has more to do with the temperament of the individuals than the sex.

I'd recommend reading extensively ahead of time in preparation for the blessed event. It will be weeks of anticipation followed by moments of sheer terror and weeks of caring for the puppies.

If she isn't actually bred at this time you might want to have her evaluated as a breeding candidate prior to breeding her. Wish you the best.