How fit is she? If she is quite unfit, she may not be able to balance on one ski long enough to get off that uphill inside edge...or at least thinks she can't.
How well do her boots fit? If they're a comfy, loose fit, she may not have the support to do anything that feels brave or daring to her. As always, get boots as small as possible without discomfort (forget shoe size and go by feel). One pair of medium thickness socks only, no pants or long johns inside the boot, and the boot buckled at tightly as possible without discomfort.
Now, try sideslipping on a slope that is steep enough (never too steep), with snow that isn't too wet & grabby nor too hard & slick. Try traverses where she rides her uphill edges. After the traverses, try garlands where she varies the direction of the traverse slightly by the tipping of her uphill ski (lifting the big toe edge higher or not so high). I all this is starting to work, try J-turns where she skis down, turns, coasts uphill, turns down, turns the other way, coasts uphill the other way, etc. Be sure you pick terrain that is just steep enough to get the maneuvers done, and not so steep that it's outside her comfort zone.
Harb's online lessons are very good. Even better is his DVD and book, Anyone can be an Expert Skier -- 1
. Yes, there is disagreement on this forum about the wisdom of Harb's system, but I find it to work very well.
A top notch instructor is a very wise choice, but an instructor that just demonstrates how to ski and doesn't really know teaching techniques to get a skier out of their rut isn't worth the cost. Level III means that the instructor has lots of experience and passed tests. Some are very good. Some aren't that good at getting results from students. Watch from afar. If you get an ineffective instructor , complain and demand a refund.