ESH. She sucks for obvious reasons.

You suck for bailing on a job you committed to. You're a professional, that was a very unprofessional move. (I know you're 18, but you're being paid to do this work, you're a professional.) As a fellow creative professional, I completely understand why you were mad and did what you did. I'm sure there was some real satisfaction. Lesson learned: never start work on any project, and don't buy supplies for that project, without an agreement in writing and a deposit. I think a 20% deposit is good, it's not an unreasonable amount to book your time and skills. It's more about the intent to pay than the money itself. Someone who balks at the deposit doesn't intend to pay you at the end of the project.

You could have also worked with her on a scope that was more reasonable. (Printing menus from your calligraphy instead of writing out 200 of them, for example.)