She's lovely and has a smile to die for. However, you asked for C&C so ...

She's sitting square to the camera which makes her shoulders look big; also her knee and, even more so, her foot. It's a distortion thing that is a very common mistake (I used to do that, too).
The chair ... if that's all you could find and she has to be seated, OK, but it doesn't in any way relate to the
style of her surroundings and it seems to clash.
The background I quite like, nice use of depth of field and the way it's dark against her lightness is nicely done. I quite like the desaturated background but you've lost her skin colouring and kept the colours in her blouse. If you've kept the original you could add the colour back to her skin without too much trouble. I'm not a fan of the vignette in this case, I think I'd have cropped quite a bit closer instead. One other thing, it's a small image and my eyes aren't what they used to be but you seem to have lost some of the black in her hair where it merges with the shadow between the trees over her left shoulder, you might be able to bring that back in PS or LR.
On the positive side, you've captured the essence of her loveliness. She comes across as a warm and happy personality and lots of experts still have difficulty capturing that kind of thing. All the advice above is stuff that can be learned, catching a look like that takes a natural photographer's eye.
P.S. Your profile doesn't say whether or not you're happy for others to edit your photos, I suggest you think about that because it helps if people here can take one of your images and
show you what they mean rather than just talking about it.