She could have gone to her parents, a counselor or a trusted adult to help her manage her emotions over the situation until a better resolution could be reached.

She did. She fucking did all the things that you say she should have done. She availed herself of all the support structures you say she should have utilized, and they all failed her.

Those parents, counselors, and trusted adults could have helped her "manage her emotions" by separating her from the harasser. Instead, they put the two of them together on a bus, effectively unsupervised. She did everything right. All of the social structures that should have supported her failed, and now you're all that the most reasonable course of action she had was direct violence.

The school's actions were foolish, lazy, unhelpful, and unacceptable. In the specific circumstances she faced, her actions were perfectly reasonable.

Counter devils advocate: our legal system does allow civilians to stop a crime in progress against themselves, physically, even if the crime itself is nonviolent in nature.

For instance, If i witness someone stealing my property, I am allowed to use reasonable, non-deadly force in defense of my property. She faced serious, permanent, and ongoing mental harm, which she had every right to attempt to stop as it occurred

And the police have fundamentaly agreed she was justified in her actions, and upheld this right, as shes not being charged.

(Although personally I think they should threaten school officials with charges of conspiracy after the fact and abetting the dissemination of csam for the expulsion, to force them to recant it.)

the situation didn't just naturally become worse. it's only worse because the school shares opinions with you.

So if a man is hurt by a woman and the world doesn’t stop that harm, is any degree of harm justified and any level of force necessary to end that harm, justified?

Yes.

Society fails at justice

I see the problem. You are conflating "stopping harm" with "justice". There is a massive difference between the two concepts, and we aren't talking about justice here.

Asking police to stop the woman from keying his car is an attempt to stop harm. Asking the prosecutor to charge her with destruction of property is an attempt to seek justice. You described a scenario where the woman is actively harming the man. He is, indeed, justified in using any level of force necessary to end that harm. You did not describe a scenario where the woman has previously caused harm, but is no longer doing so.

Keep in mind that the boy on the bus was actively engaged in harassing his victim at the time his victim used physical force against him. She was not attempting to retaliate for past harms; she was not attempting to seek justice. She was attempting to end the harm he was in the process of perpetrating.