Hi Jessica,
This is a fine picture for a lover since he just wants her picture, so that works, at least for now!
However, Charles is right about the angle and the crop but centering, although frowned on doesn't bother me so much.
This picture has a lot right: happiness, a sense of future and a beautiful smile.
What it lacks is great composition.
Massive post/tree to right: that's fine for a larger picture with other interesting things going on or else to go along with vertical, diagonal or other geometrics to complete a pattern of balance the composition. However, here it is on it's own.
Now if the tree was very intreresting with branches then it would be great, but you don't show that.
Here right arm is cut off
Her sweater is not arranged neatly.
The lighting: is that mid day with a fill flash?
I'd try more pictures, say from a window in northern light with a white board on the opposite side (and perhaps a tiny amount of fill flash. That is a great inexpensive excercise where your relationship with the model will pay off.
Make a scrap book of poses you like, not of glamor pictures, just editorial pictures in magazine, photographs you see on the internet that you really like so you can emulate simple compositions. Start with a black background and concentrate on the lighting of her face and limbs and how she is posed.
If you can do this, why not post this here so we can carry on a project of getting at least the shapes and the tonalities right!
You have a willing subject, the light is free. All you need to buy is a 4ft x8ft piece of white card for here side and a 4ft x8 foot black card for the background!
Asher