Probaly she is a beginner or don’t rode the horse very often. How she fall the horse in the back isn’t good and you can see that the horse don’t like it. She has no good sit(?) in the saddle, if she had she would have stay in.
And I think a lot of people say this wasn’t deadly bc they are riders and had mutch worse or know how worse it can be to fall of a horse.
It’s something you have to deal with when your riding a horse.