As someone that has had experience with bullying on several fronts...
This was real fucked up.
Like, that ending is reeeeeeeeally fucked up. I don't like this at all.
Bullies getting what they deserve is fucked up because?
Because any kind of retaliation to bullying proves that the bullies got to you, which is only going to incur more, if not from this girl than from someone else. Not only that, but violence tends to lose you any sympathy with authority figures.
This ending is the exact WRONG thing to do against bullying. Not to mention the characters suddenly snap and pull a 180. I really hate seeing a story like this promoting shit like this