1) Shoot her from just above the knees, have her kneel, or sit down.
2) Shoot her standing next to a midget.
3) Shooting from below is an old trick and works sometimes, but when you see it done with a model that is really tall, you understand why it works so much better on a tall, slendar model.
4) Determine where she is short - short waist (distance from hips to bust) or short legs? If the former, pull pants or bikini bottoms down on hips, if the latter, pull them up.
5) Without a reference, just standing on a seamless, you can't tell how tall someone is. If you have visual references in the shot, make them things that are not known or measurable, or shoot at unusual angles so the references don't work.
6) If your subject is standing: In Photoshop, make the canvas a little longer on the bottom than the image. Then select the entire image from about the neck down. Then use Transform/Distort, click on the bottom edge of the selection, and very carefully drag it down into some of the new canvas space. Not too much or it will be noticiable. You've just stretched the torso without altering the face (you may have to touch up the edge under the neck a bit). I just had to do this to someone and it worked great. Probably added a couple inches. Too bad you can't do it in real life.
Andy Pearlman Studio