Wes said:
but you can't argue at the fact that she died from the bull.
Yes you can. If we change the outcome to her throwing herself off the ramparts to her death, would you then be saying that gravitational pull is the culprit? Or the architect? Or the Prince's ancestor for setting the castle's location?
Couldn't we blame the farmer for not fencing in his property? Or the Prince again for keeping his home close enough to a bull?
Or take into consideration the concept of manslaughter. You are driving home and a pedestrian runs directly into the path of your car. You can't stop in time and strike him, killing him. Are you now guilty for his death, or is the asshole who just ran into your car guilty?
Sometimes you have to take responsibility for your own actions, even if they lead to your own death. That is why the Princess is the most guilty for killing the princess.