I agree with Mark Whiz- teach her to shoot the positions- prone, sitting, kneeling and standing first and in that order.
Teach her about the firearm she will be using, how to load, unload, work the safety, adjust the sights, and most importantly teach her the three golden rules of gun safety first.
Teach her proper sight alignment- best for her to learn on an iron sighted rifle first, whether it be open or aperture sights- scopes can easily be learned once the basics are down.
Show her the basic positions, if you don' t know how to shoot prone or sitting, check out the NRA website for information or booklets. If you want, I could probably send you photocopies of material if you email me.
Have her work on Natural Point Of Aim- she needs to close her eyes while in position and reopen them- if the rifle points to where she was originally aiming, her natural point of aim is correct, otherwise have her adjust her position until she can open her eyes and the sights are still on target.
have her get into positions from a standing position, starting with prone, have her dry fire at a target- preferably at a blank piece of white paper at a distance of 25-50 yards. have her concentrate on her breathing- take a breath in, let it half out, SQUEAZE the trigger. Emphasize squeazing to get her in the right habit. When she become comfortable, with this, give her one shell at a time to load and shoot. having her concentrate on aiming for the middle of the paper. The goal is not to hit something but to concentrate on making the same breathing, sight alignment and trigger pull every time. With a blank sheet of paper, there is less anxiety about hitting a target or scoring rings- if everything is done consistantly, good groups will result. Finally move up to having her load the magazine and fire off a string of shots.
Remeber to keep it fun, after each training session have her plink away at reactive targets such as soda cans and clay pigeons- something that will be fairly easy to hit- smaller targets can be substituted later.

If you teach her this way, she will be way ahead of 90% of the shooters out there. Be prepared to swallow your pride though- every girlfriend I' ve taught to shoot ended up being a better shot than me