Chaturanga Dandasana or Four-Limbed Staff Pose, also known as Low Plank, is a Yoga asana, in which a straight body parallel to the ground is supported by the toes and palms, with elbows at a right angle.
This is an example of hyperextended knees. Its bad. You need to get more on center of her feel with balance dispersed on all four corners of her feet. Bend at the knees a little and lift up on the quads instead of punching the knees back.