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.
That's what I was going to say
Increase the forward lean on her highbacks.
You have to bend more, there's no way around it.
I haven't watched the vid yet, but I'm assuming she's fairly young?
Has she fooled around with the forward lean?
Most noobs have no idea that back piece is even adjustable
Unless you have done it yourself
, it's probably still on zero forward lean.
Tell her to do as many carves as she can.
Lots n lots n lots of smaller carves as opposed to only a few longer drawn out ones.
Practice makes perfect.
If she does hundreds of quick short carves, as many as she can possibly do.
She will learn @ a phenomenal pace, 2wice that of any one else she rides with.
I've seen it happen, 4 realz
Thousands of carves a day= Real good, real fast.
Hundreds of carves a day= Not so much. You see the picture.