Firstly for portraiture this is the wrong type of lens to use. Wide angles distort, especially at the lower end. Full length portraiture 50mm at the very least and head and shoulders 70mm+.
Secondly, if you look at your horizon you can see that its completely tilted. Again this is probably due to the distortion of the lens and the fact that you are shooting on a hill but it just looks odd.
And finally there is no attachment or rapport between the photographer and model. You are standing directly in front in her way as she walks towards you, yet she is not looking at you. Its a weird angle you have taken this from, as if you are slightly above her. Move back and get on your knees and have her walk towards you to fit her all in. This would also help reduce the distortion.