It's because there is no focal point. She should be the centre of attention, so to speak but instead she's one with the background so the viewer has no idea where to place their eye.
She doesn't have to fit snugly in the square (kind of like what I have in my signature... the character isn't fit into the square). Try having her come off the square, etc. Use the rule of thirds (
http://en.wikipedia.org/wiki/Composi...visual_arts%29) that's on the page too.