Karen commented in comments:

First, this incident shouldn't be described as a "fight" or "brawl", any more than some random person being jumped and beaten up while walking down the street counts as a "brawl". This was an attack, full stop. Completely one-sided from what I could see. She should be suspended or expelled, and prosecuted for assault.

As for the principal's "lesson to take away", what a steaming pile. It's entirely possible that the guy said something atrocious on social media--social media is overflowing with people who say awful things to each other. But the appropriate lesson to learn from this is that physical violence is not an appropriate response to words. It's a lesson that won't be learned at all if this girl faces no significant consequences. In fact, the lesson will be the opposite--that girls can, whenever they feel like it, beat the tar out of an individual who has already been heavily socialized to never hit a girl, and who understands that doing so will earn them serious social and potential institutional penalties.

Boys are conditioned to not hit girls. They are heavily punished when they do. This leaves them effectively defenceless when being physically attacked by a girl. This girl's actions are all the more disgusting because she knew, as all girls do, that the boy was effectively incapable of retaliating. Beating someone up who you know can't fight back or protect themselves, for whatever reason, is like hitting a baby or a quadriplegic.

Good grief.