I have a friend who is incapable of riding directly behind the boat. When she gets up she immediately rides out on her heel edge. I've tried to get her to move the handle to her front hip, but she doesn't seem to be able to keep it there. If you have any ideas i'd appreciate it.

my step mom does that. she used to be a skier. i think everything she knows is telling her to keep her feet forward, but a fin digs in and pulls her heelside. maybe the same situation?

push the front knee over the toes, that will help turn the hips some.

Have her let go with her back hand and let her body close to the boat. Have her do some carves like that outside the wake to get used to being on edge. Once she is used to it, she can try grabbing the handle with both hands and squaring up again.

+1 on letting go with the back hand... helps open up those hips towards the shore.

third for letting go with the back hand. works really well