Being a victim of one thing doesn’t justify becoming a perpetrator of something else.

From the article:

the female victim will not face charges in the attack.

She faces no charges; she is not a perpetrator. Let's be very fucking clear on this point: nothing she did has been determined to have been "illegal". Since her actions don't violate law, we are left with discussing only morality and ethicality.

tried to get others to join in

Yes, she did. The first entity she asked to "join in" was the school itself. She asked the school for help. The school was given ample opportunity to end the harassment, and refused. Only after the school's refusal did she ask anyone else to help stop the harassment.

As soon as the school failed to act, she became ethically justified in acting directly to end the harassment. She became ethically justified in requesting the help of others to aid her in that effort.

Your entire argument stopped being valid the moment the school failed to adequately intervene against the harasser.