Agree with the barefoot comment, and I have kids doing warmups (but not plyometrics) barefoot.
Have her concentrate on a shorter stride and higher cadence (>180) during warmups and easy runs.
So-called relaxation strides, which can be 50-200 meters and not fast, where you concentrate on running with perfect form.
Certain drills, such as high knees and quick feet, which encourage forefoot striking if done correctly, thus not overstriding. Also stepping over the knee with the opposite foot/ankle.
When she is used to the higher cadence, do strengthening in the gym like squats (high weights, low reps) and step ups, and plyometrics like horizontal standing long jumps (5-6 jumps in succession with 10+ meters of total length) to increase stride length at the improved cadence.