Someone here posted a good trick a few years ago that has stuck in my head. Have her ride while holding her lead pant leg right above her knee. This will cause her to lean forward and put more weight on the front foot.
edit: it also has the added benefit of keeping your upper body quiet (ie not swinging arms, etc)
You and her are on the right track. My wife if very receptive, but not into the reading of forums, so I do the reading. The fact that you also understand that it is her fear that puts the weight on the rear foot is huge and it is not about technique but mental limitation and you have to address the confidence.
This is how I taught my wife , some will disagree with my technique. She stared about 3 years ago and we only do about 10-15 days a year.
Teach her to do one hard carve at a time on a steep blue. Draw a simile in the snow. The only way to do this is with proper balance. If you put too much weight on the back it become a skid. I had the luxury of doing this at an empty resort since we go from one side of the run to the the other side. You can do this on steeps since you are controlling your speed from the beginning.
Aiming from the other side of the run is key in trying to prevent the board from skidding.
Heel side - this is pretty much what I told her: You are going to end up of by that tree. Stand and aim the board straight down the mountain, you will gain speed, then start to sit in a controlled way, like if you forgot to check if the toilet seat is put down and you need to get back up. (Personally I don't understand why women don't alway check if it is down). In the process of sitting still aim at getting over there to that tree. By aiming for that tree, she will automatically keep weight on the downhill foot. Now to end the carve just gracefully sit down all the way and fall and admire the simile your drew in the snow. Using the curve to slow herself she will gain confidence.
Toe side is a little harder to teach her but when I told her to initiate the turn from pointing the board straight down hill, it is the same subtle motion of a forward roll, you bend your knee waist, and drop shoulder your weight over your down hill foot. It is just the beginning motion, don't drop and attempt a roll. Just to the point where you fell weight on the ball of your down hill foot. All of this created an over exaggerated movement but it gets the job done. She pointed down hill, took an athletic stance bent over, dropped her left shoulder over her left knee , drove her left shin into the tongue of her boot , the weight went to the ball of her left foot , she held the position, made the board do a high speed carve and got the board to go back up the hill. She was so excited when she felt the g-force in the carve.
If you just sit without aiming for the other side of the run , you will just skid. If you aim for the other side of the run without point the board downhill first , you will hot have any speed to make the carve. It took me 20 minutes to type something that took an instructor 2 minutes to say. Maybe a joint lesson would be good.