Assuming this is High School or your local equivilent; in my experience if you send such a letter you're simply inviting trouble for yourself. I was that guy at my school, constantly rubbing the teachers and administration's faces in the fact that they were grossly unfair. It was entertaining, but pointless. They threatened to 'hold my diploma' in the end and I threatened to humiliate them by publishing a few choice bits of particularly pathetic information in some local papers. We settled on inactive mutual animosity and I moved on and found more important things to do with my free time.

I advise your friend to do the same. Yes, it will be hard on her, but spending her last year fighting a batch of fools locked onto a particular course won't be any easier than just going on and getting started with her second chance.

Good luck.