Whoa, please post smaller size ~900x1200!
There's great warm light, that's a big plus. She has a great expression and this is simply pleasing. However, the composition should be vertical. The background is blurred beautifully, but there's too much of it. Also, move your subject to the side a little to accommodate for the rule of thirds, which makes for more dynamic composition. There's too much space above her head as well. I suppose landscape orientation would work if you cropped off some of the right and top, but don't put them too close to that edge. Also, you wouldn't want to crop the left because that's the way she's facing and that just doesn't work. Please post a crop, so we can see. Great quality photo.
It's a little too warm for my taste. Try cooling it down just a tiny bit and see how it looks. I agree with CWBaker also, it needs to be cropped. They're just about dead center in the frame. I would crop it, leaving the background on the left, but take it down to a little above her head (right around where the horizontal line of highlights is in the background) and in from the right to where the tree trunk is in the background. That should put her eyes in the top right power point of the frame.
Resize the photo so you don't have to scroll Jeez what screen resolution do you have your computer set to? I have a 17 inch monitor here at work and it fits fine (1280 x 1024) is my res. I would increase your resolution.
As for the photo, it is a bit warm with blue tint to the shirt. I really like the Bokeh from the lens though. Overall it is nice.
The elbow needs a little more room. Touching the edge like that brings it too much attention.
I think it would have been more flattering to her if your camera was higher, say around eye level. That would cut down on the "up the nostril" look.
I know this was probably an extemporaneous photo, but a different wardrobe would help. I don't think women should be photographed in sleeveless outfits if at all possible. The amount of skin competes with the face. Also, it makes the arms look larger than they actually are, which is not the effect you want with most women.
The background is really interesting, almost too much so. I just love the effect you get just to her right. Maybe if it was toned down a little by either making it darker or by a little desaturation you could keep the nifty elements while having it distract from your subject less.
Jeez what screen resolution do you have your computer set to? I have a 17 inch monitor here at work and it fits fine (1280 x 1024) is my res. I would increase your resolution. 