This is very lovely. The girl seems so emotional and lost in her own thoughts, and yet if you stare at her face more you can see a little smirk.
You picked a gorgeous model and setting for this.

I do like how you made the far away butterflies a little blurred, it made it more realistic with the foggy background.
It would have been nice to have the close up butterfly a little more saturated and vibrant. I know you are trying to make the model the main focus, but if the butterfly was a little more vibrant it makes the eye move around the entire piece.

I love everything about the girl, however her hair should be a little darker. It doesn't look very natural and should also be blurred a bit more so it can look softer. If it were to be a bit darker than it would make her skin glow just a little more and bring out the blush in her cheeks and shine in her eyes.
The front of her, closer to the tree, should have a little more shadow due to where the light is hitting, which seems is behind her.

The impact of the entire piece is breath taking and just lovely.
Just a few more shadows and making the hair more natural mostly.
The butterfly on the other hand doesn't really matter as much as the focus.

Again, you did great with this piece.