Edited to Add: I have no doubt that if I had been attacked like that as a teenager, I would have fought back within an inch of my life, and so would my own daughter. I'm sure we would have been trying to pick up that table and hit someone with it. But not every girl is going to fight back, and bullies can always pick out a victim. If they had picked on this girl before and she didn't fight back, then they knew they had easy prey. That in no way justifies what they did. I think that girl was in shock and couldn't believe what was happening - who can?
I applaud your mindset, but I think you underestimate the amount of pain that was induced with just 1/10th of the blows this girl took. Also, she was in survival mode, do what you have to (or not), to stay alive. I think in this case if she had fought back she would be dead.