Portraits are about capturing the "person". If you look closely at these you would probably agree that she has that "waiting for the camera to go off" look on her face in every shot. Never let your subject know when the camera is going to go off, interact with them and shoot when they look good.
Interaction with your subject is number 1 for successful portraits.
As for constructive critique.
One is in a weed field in harsh light, is the first thing I notice. Not a successful portrait.
2 has the most potential from your set. The scene is ok and light is ok. Camera did not go off at a flattering time to flatter the subject.
3 has some potential but shot at the wrong time of day the light is to harsh.
I think you have something good in #1 but I'm distracted by the bush covering the guitar case. In #2, her body is too stright on to the camera. A little turn and head tilt will add a nicer feel. Keep up the work!