It's true Yorkies don't have an undercoat and can get cold faster then other breeds. However, I think a lot depends on the individual.
My Annie would swoon and act as though you were trying to kill
her by asking her to go out in the winter to potty. Yet she refused to sleep under any cover at night no matter how cold it got. She simply would snuggle up closer to my neck.
Boo is all about the outdoors. Loves to be there no matter how cold or hot it is.
Just no rain please, sugar melts you know.
Yet he will only sleep far under the covers pressed tightly to your legs.
Gracie Ruth seems to be a mix of the two. She LOVES the outdoors, cold, hot or rain, she loves it all. She started out sleeping uncovered by my neck, but recently has been moving to under the covers with her head poking out.
I'm waiting for her to ask for her own little pillow to put her head on. lol
I'd just watch and see how your girl acts. I'd probably have some type of coat/sweater ready just in case you need it. You'll know when you open the door if she thinks it's too cold. And just like we have to watch out for them in the summer to not get overheated, watch to see that she doesn't stay out to the point of shivering.