Welcome to Yorkie Talk! When Max was a pup, he was terrified of walking on different surfaces. Pavement was okay, but then he had to get used to grass, cement, brick sidewalks. He was almost 1 before I started taking him into town to walk, and he was overwhelmed by the people and cars.
Keep doing what you are doing, taking it slowly, not pushing her. Baby steps and lots of praise and rewards. She will get there.
Might also help to just sit on a bench holding her a little to watch the traffic. Make everything a positive experience.