Get a harness for your Yorkie first and foremost.
Now get a CHAIN leash. One with the smallest links. Cut off the leather handle as you will never use this one for walking anywhere AND she will most likely chew it which is not good for her.
Third put her harness on and leave it on. She needs to get used to the feel of it before you go to the next step. Let it be on for about a week - so she walks and runs in it without any problems. (you can take it off at night when sleeping)
Fourth. After she is totally relaxed with the harness being on, clip the leash onto the harness and leave it drag on the floor. This will teach her the leash is not something to be afraid of. It will follow her wherever she wants to go. DON'T pick her up to take her someplace MAKE her walk. Keep her food and water bowls in the kitchen. This will make her walk out of the living room to get something to eat and drink.
STOP SPOILING HER. She has you right where she wants you -- wrapped around her little paws!
Once she is walking around with the chain dragging behind her without any problems switch the chain to her regular walking lead and again allow it to drag. This step MUST be done only when you can watch her.
After about an hour, pick up the lead and follow her. THEN you turn and go back in the other direction giving her a treat as she follows you. You will need to do this for about 3 days.
Now start taking her out the door and back. She will quickly catch on that the leash going on means spending extra special time with the person(s) she loves most. Reward her every time week one, every other time week 2 and so on, Then only when she comes in from a nice walk.
If something frightens her about walking stop and let her investigate the area/object on her terms. NEVER yank or pull - this will only make her put on the skids. Keep the lead loose.
This is how my trainers MUST work with a leash shy dog. We raise & train service dogs for physically disabled as well as assist with owner - trained dogs.
REMEMBER: Animals understand Tone and Body Language long before understanding our words. Animals do NOT understand our language until after training.