I'd like to start first off with a reminder of the conscientious ettiquette policy. Let's keep things friendly here and use this video as a way to educate people and not attack.
As for the rearing horse, I watched the video. The first rear was completely the riders fault. As for hitting the horse on the head. I'm the owner of a rearer and I can promise you that it is a very dangerous habit. It's also a hard habit to break, with some horses it is un-breakable.
This rider is the cause of the rears with her heavy handedness and her riding style. This horse could probably be fixed with the right rider/trainer combination. However, when a horse rears, hitting it between the ears IS a tried and true method. However, this rider waited way to long making the punishement have no meaning what so ever. The thought process between hitting a horse between the ears is that the horse thinks it's hitting it's head. It has to be done on the up-movement and it has to be ONE solid hit. That's it. It doesnt even have to be HARD, but it has to be timed perfectly. This rider waited until the horse was on the ground before smacking and then she just hit every which way. Not a good method at all.
She also is not using any counter measures.