I told a girl in my class (9th grade) that if anyone saw her school picture, they would vomit (to make matters worse I made a gagging motion.) Of course, she is gorgeous, it was a joke. A very foolish mistake on my part... she now hates me (as far as I know) and doesnt talk to me anymore. What should I do to revive our friendship?
Apologize. Tell her exactly what you think. It sounds like yo realize it was offensive and inappropriate because she took offense to it. Tell her your sorry and that she is, in fact, very beautiful. If she doesn't accept your apology then give her time, and just continue to be nice (don't say something like, "well then fine you are ugly" .. etc).
If she doesn't forgive you then thats her problem and she has an ugly personality. Don't bother yourself with someone who can't forgive, obviously don't flaunt that point of view in her face if she doesn't forgive you. That would be counter intuitive to the idea of kindness and forgiveness.