I'm sure she will do just fine -- she is an average sized yorkie and they are spayed all the time, even much smaller. Just make sure you have a vet experienced with small dogs and that you trust. I do understand how you feel though! I have finally scheduled my little Annie for her spay surgery. I am overdue but I too, was feeling the dread of a tiny girl going under anesthesia.
Logic tells me that there is much more danger in NOT doing it than there is in just getting it done and over with. But my heart would break when I looked at her and thought of surgery. She is just such a baby.
But it is high time I do the responsible thing that I recommend for others and take care of my pup! I had to wait til next month as the doctor I want to do it was a combo of booked & out of town for April. But my 3 pound gal will be spayed in early May. Worth the short wait for me to get the vet I trust the most -- he barely leaves a scar and all the dogs I know of going with him have had such quick recoveries! That takes away a lot of the worry. I'll pray for your little girl and maybe you can send some up for Annie next month.