Take on Rosalie's blond hair. This is her most identifiable trait, as it is what sets her apart from others in her family. You can either buy a middle-back length blond wig or straighten your natural locks to look like hers. To color your hair, visit a stylist who can help you achieve just the right shade.
Wear contacts that are amber colored. Since Rosalie is actually a vampire, her eyes glow like the color of flames. They are another one of her most distinct traits.
Use black eyeliner to enhance your eyes. Rosalie doesn't appear to wear much makeup, but her eyes are defined. Also, use the black eyeliner to dot on a faux mole on the right side of your mouth, just above your top lip.
Complete the makeup look with a simple peach lipstick. You don't want to take the attention away from the eyes and hair.
Layer a purple long sleeved shirt under a grey tunic. You can improvise with this portion of the look, if you don't have these items exactly.
Complete the outfit with dark denim pants. Black pants or dark leggings also work well.