Sounds like she is trying to rush and doesn't know what a full twist really feels like. She just needs to keep practicing, and if the gym has an overhead rig it might be worth a shot to fully turn a few.
If her body understands how to initiate, then its not a technique issue (most likely).
She is stopping early because its been keeping her safe so far - why ruin a good thing, right? She needs to know she will be safe by holding on just a smidge longer, and that comes with experience.
At least, that's my interpretation..
Good luck!
Ryan