Composition: get rid of or don't include the tree, in this case it adds nothing to the image - she has nice hair, so turning her a little more front ways would help fill out the crop shape and size that you chose.
Exposure: underexposed although, in a shot like this depending on your processing abilities, the background would be ok at the present exposure
In other words, had you exposed a little brighter, you could have brough down the background so she would stand out.
Focus and any retouching on the skin looks good