You need to get some light into her eyes. In the first two, she has just two black holes instead of eyes. The eyes are the windows to the soul and in photography, typically, if the eyes are not in focus or visible, then the whole image will appear lacking and/or out of focus (given this type of overhead sunlight lighting her). A reflector will be your best friend in open sunlight or, better yet, look for open shade and get some light into her eye sockets. The third one is nice and there is more light in her eyes. The only thing that bothers me about this particular image is her placement. While her body is in the left 1/3rd of the image, her head and eyes are smack dab in the middle and make the image very static. If you crop it so that the edge is much closer to her right arm, she'll be at the left-most part of the image and the tilting of her head will be toward the middle of the frame and draw the viewer in more.
Just my .02 for what it's worth. She has a beautiful smile. Please post some more of her!
Thanks for sharing!