Does your dog like toys? The best reward might be a little game of tug of war with a toy! Are her treats something completely different. IE not her kibble? Something super tasty that she ONLY gets when you're doing training.
And the training has to be fun. Keep training sessions short. Get her to sit twice in a row and leave it at that for 1/2 an hour then get her to sit again a couple of times. I find myself "nagging" if my two don't do something and they just get frustrated with me and I have to stop.
Yorkies aren't untrainable but terriers do take a little more patience
. You see people that are used to collies and the like and they just don't understand the terrier mentality.
Best of luck with the training. A little basic obedience makes for a much better relationship between you and your little pooch.