The fact that the horse was able to wander off, was on her. That was her incompetence, and irresponsibility. The horse doesn't know that it could have caused an accident. It had no malice, no intent, and certainly no understanding.
If you allow a toddler to wander off into traffic, who is responsible for that? The toddler? No, the parent that should have had a firm grasp on their hand, or ensured that another responsible person had a firm grasp of their hand.
That was NOT discipline. That was temper. Beating a horse about the head is never okay, it's the best way to make a horse headshy. Kicking a horse in the chest is just fucking ridiculous. She was having an adult sized toddler temper tantrum, and taking out her fury (most probably truly aimed at the Hunt Sab's, rather than the horse) out on the victim that couldn't/wouldn't strike back - the confused, well bred, and well trained horse.
Well bred, and well trained - well, the woman certainly isn't. If your toddler wanders out into traffic due to your negligence - is the appropriate response to beat your toddler about the head and kick them in the head? No? Then don't do it on an animal equally dependent on you doing your job to keep them and others safe as a toddler would be.