If the high chair to the feet and legs to make fatigue to fly back. If the Chair to the floating knee or shorter and she will dip into water on the seats make it painful and butt.
If the high chair to keep your feet will float on the leg and back pain. If a low chair, it would float up and the bottom of the slope, only to dip on the seat ache and sore bottom.
If a high chair to the foot will float the legs and back pain. If the chair low knee will float up and at the bottom of the steep, only to sit on the seat bottom ache and pain.