That's what I was going to say Increase the forward lean on her highbacks.I think she needs to bend her knees a lot more. Especially on toeside turns. Like Wrath said, push her to harder terrain, like blues. Tell her to bend her knees as much as she can, like she's sitting down in a chair. That helps her get a more aggressive edge angle and "carve" a bit. She won't truly be carving, but it'll improve her turns. Get her more comfortable at speed as well. Speed helps you, but people are afraid of it. With more speed, your board can go into a turn much easier and it will help her get more confident on a board. Try increasing the forward lean on her bindings. It forces her to bend her knees and have better form.
I've made both my friends do this when I taught them. Hiked the bottom of the shallow hill and began one footed heel and toeside stops. Both of them had heel/toeside turns their first day! Glad you make me feel like I've done something right anyway.. off subject.The first thing I would advise is to have her work on "front foot steering" The best way to get someone to feel this concept is to go to a super mellow slope and ride it one footed.