What a wonderful image of this girl.
You have got great eye contact with the subject and a lovely natural smile.
The background is not too distracting and well out of focus.
How could you improve the image? Apart from a bit more space above her heard, two points that would improve the image IMHO.
1. A crop to the left of the image would remove the distracting highlight at the top and would also improve the composition, moving the girl more to the left and having all the negative space on the right.
2. The hard shadow made by her nose, is also distracting. This could be corrected by using a reflector to "fill in" and soften the shadow, or you could take a couple of steps to the right so that the sun is lighting your subject more evenly, and then getting the girl to look at you.
I hope this helps,