OP, I'm sorry 90% of the people in this thread are being assholes. I'm a recovering bulimic myself and I know how hard it can be. If your mom doesn't understand, please seek therapy so you have someone to listen to you and help you through these difficult times.
And to everyone giving her crap for "wasting food middle Eastern kids could eat," it's not as though she's physically stealing food from underprivileged. Her not throwing up her pizza isn't going to buy one for a refugee camp. If you're so concerned about starvation, donate food or money or time to charities helping them instead of sitting around mocking someone on the internet. You might think you're Mother Theresa, but bitching on FML isn't putting food on anybody's plate.