The way I teach this is to get a block mat about hip height of the gymnast, and have them jump from the floor to the mat with hands and feet on the mat.
Ideally (I know this sounds silly) I want them to be able to do this with straight legs - this means, they will end a pike sit position, standing on the block (or, a pike with only hands and feet on the mat, hands flat to palms).
If they can do this with their legs straight, it will re-inforce the idea that the shoulders need to go forward, and the hips need to go up. When they get to the bar, I transfer the same idea - hands and feet together, then stand up. Many girls are taught to "hop" right into the squat on, which brings a lot of fear, and I find a LOT more success building up to that hop mechanism, if I ever push it at all. I think squat ons look better when they look safer, and my heart doesnt flutter wondering if their feet will catch the bar.
Something she can do at home is something called "bear hops" (at least, that's what I Call them). Basically, she starts in a push-up position, with arms extended, dip the hips a bit to pop them up, and pull the feet towards her hands, ending in the same position with her hips up and her feet next to her hands. The reason they are called "hops" is that she can drop back to prone, and repeat for a great exercise that will lead to other skills (like presses, and cast handstands..)
Good luck! I hope this helps.
Ryan