Dear Doc;
As you may know, I am one poster that posts a lot of research on spaying and neutering.
First the risks of the surgery, especially with pre-op blood work are very low. In our library we do have the recommended anaesthesia protocols.
At 17 months old her long bones are all grown, her physeal plates have closed, so the ortho risks are at a minimum.
But do know that spaying or not, mammary tumours can occur, and as an owner of a female, you need to palpate 8 nipples at least monthly to check for irregularities. You can ask your vet to show you how. It is easily done and can become part of your weekly grooming routine
Mammary tumours do occur with greater frequency in un-spayed and un-bred females, so keep that in mind.
I think quite frankly as a pet owner, given we have no research on Yorkies in this arena specific to the health risks on spaying Yorkies at what-ever age, it is best to spay her.
It frees you to not worry every 6 months or so from keeping her safe from un-wanted breedings. I think that is the main benefit to you.