The point of view looks like from the height of her eyes: the horizon should then be at that height too.
Since this would not be very nice, you might raise it less, maybe btw breasts and shoulders at breast height.
It will help with the gun butt too, which looks like a house on the horizon.
Anatomy is way off, Jorund's edit helps but doesn't go as far as needed with the arms. Won't say more about it, I'm not good there.
You give the bg a constant amount of detail btw the foreground, and the, well, bg (plants and such). Try to make detail fade away into simple flat colors as you get farther.
A forest is a good idea, think of a misty one, with just a few silhouettes of trees.
Also, you should probably keep most of the warmer / more sat colors for the girl and a few foreground highlights, and leave the bg to the coldest.