How should I tell this bitch of a woman off?

Aww, it seems like it's too late to offer my advice. But it seems you're doing what I would've told you to do: try to find out how she feels then send her on a guilt trip by telling her what you thought about her in the past and present. Oh yeah, blocking her is like a sign that you're remembering her. Deleting her off your buddy list would be better since you just don't need to see her name.
And for the teacher, (if you want to be an ass, but i don't think you're one) you can go to the school and tell the students, "Hey, you know Mr. ____? I heard he's going out with a 20 yr old who used to come to this school." Sounds immature but revenge is fun.

Jam it back in, in the dark.