As she gets the feel of the correct position, and knows she can make it into the pit ok, you can gradually move her step back and grip up. The is a task progression method. She must perform this properly X number of times correctly. If she does, move up and back. If she goes back to reaching to be under, start again from the beginning of the drills.
Coaches must be aware....for a vaulter to simply move back to the correct take off position, it is very difficult. One foot difference in the takeoff area can feel like the difference between the north and south rim of the Grand Canyon to the vaulter. Slow, steady drills at low grips on proper takeoff marks will come with patience and lots of repitition.
This is very well said and very true. The repetition and patience is very important, and while it can become dull and boring for the athlete, it can get frustrating for the coach as well. Keep repeating the simple drills and slowly progress. I use the term baby steps of progression. If each drill is slightly harder than the next, we take baby steps forward. Sometimes "life" can happen and we must take a couple of "steps" back. Baby steps back is a lot easier than large steps.
While it may take some time to work and see a change, the feeling of seeing your athlete take off correctly is a beautiful thing and makes all the time and energy worth it!