you're 13, finish school. i hate to say it, but your mom is right.
yes a talent agency might help, but once you're looking for a job in the city and trying to survive, where will you be without even finishing middle school, let alone high school?
do as much as you can in your area -- community theatre, summer stock, your lessons, maybe even a few professional open calls if they come around etc. i know it's not "the big time", but getting connected with a talent agency doesn't secure success.
you can want it really really bad, trust me, a lot of us understand that sentiment. you just have to make a compromise and look at the long-term consequences.
"grace, you're stuffed in a box getting rid of ass plaque. let's face it, this evening is a bust."