Using the sun to ascent the model's hair can work great...but you need to light up or expose the face a little more...otherwise the face just looks dark...as it does here. It can be nice to have flowers in the background...but in this case, the flower is brighter than her face, which draws attention away from the face...which you don't want to do with portraits.
The directional quality of the light is nice...it create a modeling (3D) effect on the face of the model. In this case, it looks more like broad lighting than short lighting. Short lighting may have been more flattering.
Keep shooting and trying different things.