Very nice! And I ditto your comments, @timtam. Even though there’s not a lot of contrast, the B&W still works, especially the darker hair against the bright background on the right side of the girl.
Cropping the dark line at the bottom of the image is great, but in my opinion, I liked the top section background in the first image where it seemed like there was something for the girl to be looking at. Perhaps removing the dark triangle at the top right of her head (with a clone or spot-removal tool) would help to eliminate the feeling that there are so many distractions back there.
The centered, vertical composition works very well here, especially since you can see that her arms are bent forward (indicating that she’s doing something innocently with her hands, hence the appropriate title of the picture). Taking a horizontal shot might completely change the feeling of the picture, but I would be curious what it would look like, especially if there was something of noticeable interest for her to be looking at, such as another person or a sunset.
On a final note, take a look at this great article on converting your color images to B&W in Lightroom: http://layersmagazine.com/create-stunning-black-and-white-images-in-lightroom.html Even if you don’t have Lightroom, it’s neat to see how the process works and may give you ideas for how to make better B&W images in the program that you are using.