Just because you want to teach the skills as soon as possible doesn't mean its fair to expect it will come quickly.
First like its been said. you need to teach her a Sole circle. This will teach her how to shift the wrists, keep the feet on the bar, and learn/feel how to work the bar (the flexing the bar). This is important.. This should really be your first line of drills..
In the mean time you should be drilling in a late toe on drop, well as late as you can, but it depends on the kids ability/level of conditioning as well (won't go into technique as i will assume you are aware of the technique since you coaching it, but ask if you need more detail), as well as the opening and the drop from HS using a variety of drills (there aren't really a great deal of them so i am assume you know them)
When she can do continuous circles with some amplitude (preferably bar flexing) its safe to say she is ready to work the actual shoot, and to introduce a toe on action. Always remember to remind the gymnast to try and snap the feet UNDER the bar, onto ontop. If she puts the feet to early/ontop of the bar or on the side, generally the feet will want to come off on the opposite side (Action reaction), hence why the bar flexing is quite important.
Introduce the actual tow on from a smaller cast (like from 45deg) and spot, also do sole circles into shoot. (With and without spotting, or using straps or all three depends what is available to you). And when all this done you can add from HS, because from here the fear factor kicks in, and feet coming off here can also be a reason for it.
I won't talk about the actual shoot as you didn't ask about it.