Teresa,
There are many very well informed people on this Forum, but, when you speak... I listen ! So having said that, I have a question for you, and it's "sorta" in line with the Topic here. I've owned many Breeds and even more Dogs in my life, and as I've said before, Yorkies stand out SO far above the rest, I'm just amazed by it. But, I've noticed something, which it will take someone with considerable experience to comment on.
So here goes...
I think, IF you Spay a Female Yorkie, before she has her first heat, that the probability of her being "aggressively" dominant is very likely.
Conversely, if you wait and Spay after she heats, she will be MUCH more passive in the Pack, and allow another Female to be Alpha with no or few problems.
I know this sounds reversed, but, I think that a Female recognizes the loss of being able to reproduce, and it sets her back psychologically, causing a more passive nature.
Whereas, the one who never knows, isn't effected by having had that ability taken away, and steps up and is much more likely to want the Alpha Roll.
Your opinion ?
PS:
This has nothing to do with the abilities/desires of an intact Female.
I've been accused of "over thinking" things by the best !