She was born on December 28 , 1981 in New York City , United States to an American father and South African mother . Miller has starred in Layer Cake , Alfie , Factory Girl and The Edge of Love . Sienna Rose Miller ( born 28 December 1981 ) is an English actress , model , and fashion designer , best known for her roles in Layer Cake , Alfie , Factory Girl , The Edge of Love and G.I. Joe : The Rise of Cobra .