To complete her report card, give her a grade for content and a grade for effort.
Dear Shirtless,
While I was not the intended recipient of your picture I thought it might help if I gave you a few pointers. For one, the lighting is too dark and your breasts tend to look uninviting. Two, you should move the camera down. I'd rather see your stomach than your neck. Three, pull back a little as the close up makes everything look out of balance.
I hope you take my advice under consideration. If you do your boyfriend, and all of his pals, will be masturbating to your picture in no time at all.
Grade for Content: D
Grade for Effort: C