If you have
trouble balancing in Vrksasana, try lowering your center of gravity
by practicing the pose with your standing - leg
knee slightly bent and the arms in a lower position.
For her, based upon my experience coaching her, I also know that she has
trouble with posterior chain strength & engagement, so her tendency is often to take tension off of the hamstrings and glutes, which she does in this video
by quickly extending the
knees on the first pull and shooting her hips too high.