This is a good example of what portrait photographers call Rembrandt lighting. In simple terms, the main light comes from from above eye level and from the side. This results in one side of the face being fairly bright and a splash of light highlighting the cheek bone. This lighting thins and flatters the face, although Jessica's classic good looks needed little flattery.
Incidentally, this photo shows the result of a fairly strong soft filter applied in Photoshop. So, contrary to what I said a couple days ago, I do blur reality once in a while. I just thought the effect made this portrait a little more glamorous.