Start with the fundamentals: stance, grip, bridge, stroke.
Stance - find something comfortable, which allows the grip arm to swing freely and the head to be aligned. You may also have to take into account the "boob" factor (not trying to be funny, it's just a fact of life). Allow her head to naturally go where it wants to go - don't force her to have her chin on the cue, or under a certain eye. I've found that just playing with foot alignment will cause everything to fall into place.
Grip - again, find something comfortable, but avoid the "death grip" at all costs. Stress the importance of a loose grip, one which allows the wrist to move and compensate naturally to keep the stroke level. Proper grip location is dictated by height, arm length, bridge length, etc. Ideally, grip location will allow the cue to contact the CB when the forearm is perpendicular to the floor.
Bridge - an oft-overlooked fundamental. Make sure that she knows that, whenever possible, the entire hand should be on the bed of the table (lots of beginners like to have the heel of their bridge hand up, for whatever reason). Start with the open bridge, concentrating on a well-formed V, with a rock-solid foundation formed by full contact between hand and table.
Stroke - practice makes perfect. This is not something anyone is going to learn in a week or two. Concentrate on allowing the cue to flow naturally. Don't try to control the cue through the stroke (too tense). Allow the cue to come to a natural stop (no herky-jerky). There should be a defined transition from address, to backswing, to forwardswing.
Having a solid foundation in the fundamentals is paramount. You don't want to work on a shot, then adjust one of the above - the player will have to re-learn the shot. Start with the basics, then work from there. It's a cliche, true, but before you can walk, you must learn to crawl.
-djb