How do I make my dog understand what side of the sidewalk to walk on?

When training "heel", if she gets ahead of you, without a word or any other signal, make an instant about-face and briskly walk in the opposite direction. This will surprise her and make her pay more attention to where you are - the only way she can do that is not to walk ahead of you. A little harder to do with a small dog, but accomplishing the same thing, is to turn left abruptly when she starts to get ahead of you. Your right leg will swing around and bump her nose.