I know this isn't a critique thread but since this is a possible safety issue, I want to tell you that your friend should ask a trainer to work with her and her position. She was holding her reins much too tightly and that could only have agitated the horse. Also, when a horse balks, you should turn the head to the side with one rein (as you don't want to trap them with the other) and leg yield or circle if they won't go forward. She pulled straight back, and it only invited him to react further.
"The trouble with the world is that the stupid are certain and the intelligent are full of doubt"