Sienna is no "Lady"
Just because you’re friends, doesn’t mean you aren’t in competition. Sienna Miller is supposedly “totally miffed” about buddy Keira Knightley being in final talks over the remake of “My Fair Lady”. Sienna is said to have told Keira that she wanted the part, and was even taken voice lessons to sing in the role.
That’s just the way it goes Sienna. And somehow, even though you’ve both gone topless in movies, it’s still easier to see Keira as the “Lady”.