I'm not exactly a "professional" artist, but I must say that this piece blew me away.
The coloration, the smooth lines, the contrast...all added to the beauty of this photograph.
The dress worn by the model and the lack of shoes give this piece a sophisticated yet care free vibe, which is hardly ever accomplished tactfully. Adding to this is the slight misalignment of the model's dress strap and the wave to her hair. I get the impression that she is waiting for something...ever so patiently.
Anyways, amazing job. I love this through and through and you should be proud of your work!
addendum: alternative, you could greatly extend the left side and crop a little tighter at the top, leaving the lower right corner where it is, so that the top left corner will fall on a line drawn from the current lower right corner through the lower right corner of the model's triangle. That might work better, and add a more dynamic imbalance to the dark negative space, possibly creating drama or an implied meaning to the overall composition.
on looking at it further: 1. the model forms what is essentially a right triangle 2. the reflection on the floor is not evident enough to alter the basic composition of forms 3. the diagonals of the crop do not "agree" with or line up with the sides or corners of the model's triangle. I think that is what bugs me. If you can, please make another crop in which the top and left borders remain where they presently are, and the lower right corner falls on a line drawn from the upper left corner through the lower right corner of the model's triangle. I suspect that will look better.