You need a larger DoF. Try F.11 to F.22 as a bench mark for portraits.
Use a srim between natural light and the model to soften the highlights i.e. Her left shoulder.
Consider using a soft box towards the model even if at low power to lighten her face and evening the shot out.
Its a nice pic but these points I feel could make it a great shot.
Phil
Sorry Luke I was being sarky!