I'm a girl, and I'd probably go with longer hair. Short hair draws attention to the face.
Long hair (closer to the face and neck) but in a blunt cut or jagged effect or even the "spiked effect" (the in style for young women) will help your jawline look more refined and also make you look a little taller. Look through hairstyle magazines in a grocery store or drug store or flip through movie magazines and find a style you like.