ok, please bear with me. voting this challenge is extremely difficult, not just because of the size, but because we are dealing with images that people consider their best. it makes even constructive criticism hard...
it's not that i could tell you what would make this a better image--i can't. what i can tell you is that i don't see anything in it that is going to grab me as a viewer/voter and make me go "wow!" she is a nice looking girl, and i'm sure she's capable of a range of expressions and emotions, but you haven't given me any of that. one of the 'challenges' is to pick entries that will generate positive reactions from a broadbase of viewers; you don't want to pick entries that either don't register, or worse, foster negative reactions. it is obvious that you have a decent camera, and i am sure that this does not represent your best work. with that, i'll wish you good luck with this, and better luck in the challenges to come. just think of this as a starting point for the rest of the year. good luck in the challenges yet to come!
NIce portrait, good dof, could do without the face in the background, but otherwise this is a solid shot. Also, it might be worth trying to spot edit a couple of the blemishes on her face - she is a very pretty girl, but they distract from the rest of her face a little.
I would suggest cropping off the left of this to get rid of the other face in the corner. Also, if she had turned a bit more towards you I think that would have avoided the dark shadows on that side of her face.