Christina is wearing an excellent example of the partial updo hair style.  The hair in the crown area is pulled back into a mid-height pony tail.  Her hair is slightly wavy all over, and she has side swept bangs that are cut at eye level.

Create this style on your own by applying a styling cream or gel and blow drying the hair using a large round brush.  Add soft waves throughout the hair using a medium barrel curling iron or even hot rollers.

Blast the style with a finishing spray to seal in the look.