Walk some streets that are more quiet. Present noises to her in a controlled environment, one at a time. Walking her in an area with all sorts of stimuli is only going to overwhelm her. Walk her on a quiet street and start working obedience. Itll build her confidence, build her trust in you, and itll give you more control when it comes time to start desensitizing. For example; walk her on a quiet street and when you get to a point where you are comfortable with her obedience start presenting her with sounds she would typically be afraid of. Have her sit while a car honks its horn from 25 yards away; then slowly move closer when you see she is becoming more comfortable. Then when youre done with that exercise have her sit or down while a car honks its horn AND cars are passing by from about 25 yards away (remember 25 yards is just an example. Work with whatever distance is necessary for her) and use obedience to help her overcome her fears.