I tried several quick techniques to lighten the bottom but each gave me poor results. If you have the time and know Photoshop, you could knock out the background and place her on a lighter background, thus letting her pants and feet show. Or you could do what I always do ... look for what's really interesting in the shot and crop, crop, crop! Sometimes a tight crop is much more interesting than a full body shot. In this shot, I thought the model smoking was way more interesting than her feet, so here's how I would crop it.
