The composition is superb. It tells a story...or rather encourages the viewer to make up their own story. Is she peering out the window in fright? Anticipation? Trepidation? Is she tired because the elevator is broken and she's just taking a break. Is she weary of the problems of her every day world? I suspect this picture will evoke different feelings for everyone who views it and that is one of the marks of true art.
The lines, the angles, and the geopmetric proportions just add to the scene.