Thanks, guys. Part of the challenge will be tactfully getting her to acknowledge the problem as significant enough to address with cures.
rayer:
That's the key. A shooter with a problem will nod when you describe it, repeat it back to you when asked, discuss at great length what is needed to overcome the problem, and then go right back to doing it wrong.
That's where a ball-and-dummy drill can help; making the shooter realize not only what they are doing wrong, but what happens to the gun WHEN they do it. The shooters-eye view of that front sight nosediving out of the sight picture when they snap on an empty chamber should be verbally reinforced with something like this:
"Did you see that movement? That's not a good thing. What you can't see is that when the sight moves, it actually starts moving BEFORE the bullet leaves the barrel, because it takes a small amount of time for the hammer to fall, the firing pin to strike the primer, the powder to ignite, and the bullet to begin moving. You don't see that downward movement on a live shot because the gun's recoil 'bounce' covers it up. It's very important to squeeze the trigger so slowly and/or gently that the sights (and therefore, the gun) do not move after the hammer falls."
Then you can do some dry-fire practice. Align sights, hold on target as best they can, WHILE SQUEEZING THE TRIGGER. Make it just like a live-fire shot, so the habit will transfer over to live fire without modification.
If you have a video camera, or a digital still camera with a video mode, you can record a couple of short movies of the shooter snapping/jerking the trigger to show them what you're seeing. Shoot the video off a tripod (or set the camera on the solid benchtop), viewing from the side so the gun's movement is visible, and if you can line-up the gun with something behind it (a mark on the wall, etc.) so the movement is more noticeable, then that will help your case.
If the person is still snapping/jerking the trigger during dry-fire practice, use a penny or other coin placed flat on the top of the gun once they are in position. When they can hold position and sight alignment while squeezing the trigger gently enough that they don't knock the penny off of the gun when the hammer falls, ten times in a row, they are ready to go back to live-fire.
Don't use the penny/coin on a loaded gun, BTW. It can be hard on the sights, the shooter, and anyone else nearby...