You're correct, death is not the answer here, death lets her off way too easy. Her punishment should be something more along the lines of losing a finger in a car door or something and then having the scars kind of look like your initials so that every time she experiences fantom pain she can't help but remember what she did.

Also, an enhanced sense of justice is often part of ADHD.

The entire class? That's really harsh, sorry that happened to you.