I'm not an expert. But from what I understand she should squash in the hips and chest a little. So when she is at the lowest point of her walk animation the pelvis moves down, followed by the lower chest a few frames later, then the upper chest a few frames after that.
See this animation for an example: http://www.youtube.com/watch?v=Jcpsumu4LLI
Notice how the ball kinda bounces up and down as it walks? That's because it's compressing at the lowest point and stretching at the highest point. You motion doesn't have to be this exaggerated but a little squash and stretch will give the animation life.