Am I overreacting wanting to fight a girl who is harassing my brother?

There is a girl (let’s call her Emma) in me and my twin brother’s bio class. She sits next to him and constantly messes with him. Reaching over and touching him, whispering weird things to him, etc. Yesterday though she actually took a picture of him and her and posted it on her story without his permission, titling it “finally got a picture with my new bf.” He is obviously pissed off about this because she is fairly popular and a lot of people see her story. But he also knows if he were to get mad at her she would just record that too and turn that into some story. We are boy/girl twins and he says he hopes someone beats her up. He would never raise a hand to a girl because he is male unless it were a dangerous/self defense situation. But I want to fight her. Am I overreacting? Is there something else I should do? How should I handle this, and should I handle it at all or is this an overreaction on my part?