There are three different head positions used in portraiture: seventh-eighth view, three-quarter view, and profile.
In the seventh-eighth view pose (photo on the left), you see slightly more of one side of the face, but you would still see both ears.
In the three-quarter view pose (center photo), the far ear is no longer visible, and more of the opposite side of the face is seen (the side toward the camera). The eye farther from the camera will look smaller, so position your friend so that her smaller eye (if she has one) is closer to the camera. The eyes will then appear equal in size.
In the profile pose, you only see one side of the face. The photo on the right is not quite profile because you can still see the eyelashes on the side opposite to the camera.
With all three poses, remember to keep your friend’s shoulders at an angle to the camera. It doesn’t have to be by much, though. Also, once you’ve posed her, have her move her head around and take different shots with the three different head positions. But most importantly, let her have fun. It will show, and the pictures will be better for it.