Roz, you are getting there. An improvement over the one that was in half shade half light. This images needs some more light on the face it has an overall flat look to it. A flash would have helped a bit.
As far as posing goes this looks almost like a mug shot at a police lineup. Try having her body angled maybe 20 degrees to the left or right and then have the young lady turn her head to look towards you. Also have her hold her arms out like she is carrying a box with her palms facing up, this will help the shoulders a bit.
Finally, if you do use a flash, have her lick her lips just prior to the shot, this will add a nice sheen to them so they are not so flat, the light will make them brighter. The flash should also give a nice catchlight in the eyes. The flash should not be dead center on the camera, get a cord and remote it to the left or right and slightly higher so it puts the catchlight at either the 2 or 10 o'clock position in her eyes.
Portraits can be fun, but they are also hard work if you want those glamorous results. Keep up the good work.