The general principle of ethics in martial arts is that you use enough force to incapacitate your attacker and prevent the possibility of further attack, then leave. I think doing permanent damage inadvertently in self-defense is acceptable, but it shouldn't be an objective.
In this case, she used very little force - not enough to inflict pain or damage - and her attacker was not incapacitated. Not only that, but she had no way of knowing if the other men there were his allies or might be willing to help her. Also, she was trapped on a moving bus so leaving was not an option. So, what to do? She can't leave, she can't sit back down without turning her back on her attacker and confining herself in a limited space. She has to maintain her dominant position and keep the whole group of men on the bus in her sight lines and under her control until she feels it is safe to leave. How would you do that if you were in her shoes?
I think I would have done the same as she did, but (based on the few altercations I've had before) I would have been quieter about it and inflicted more pain and damage initially - preferably enough to put the attacker on the ground. With the creepy perv incapacitated, it would be a good time to get a sense of the other men on the bus and determine whether or not they are also a threat, and if so, incapacitate them as well.