Hi and welcome to the forum. I wanted to say that I am sorry for you loss of your yorkie recently.
My opinion on the spaying is this:
Even if the new pup is male and is neutered right away, there is ALWAYS some outside chance that a non-spayed female could get pregnant. I've seen too many incidents when a dog that "never goes outside and never around other dogs" gets out by accident. If that occurred while in heat, it's just asking for trouble. I don't think there is any harm at all in spaying later in life and the risk of not doing it (even if miniscule) is there. So, I say spay.
