I would start with working on the feeling of using the hands/forearms to turn the barrel to contact. I posted a video in my comment on page 1 of the thread. Hands turn the barrel. Rear shoulder delivers the hands. Work "out-from" the rear shoulder, not around the body. It's going to be a very different feel for her, and will take a while to reprogram her pattern.
EDIT: Having her start with the barrel resting on her shoulder, and learning how to turn the barrel off the shoulder will help reprogram the DBSF move. If the barrel stays on the shoulder until it's launched, the hands can't lay it flat behind her the way she is now. Learning how to use an angled swing plane is a big part of making this work, too.
This is great.^^^^^ May I suggest long tee where she can see the trajectory of the ball. Instant feedback. She should be able to hit the ball off the tee in the air to the outfield grass. Or even better yet, put the tee behind second base and have her hit HRs. Quickest way to learn IMO.