RE: British ELLE, it was indeed Cameron's very first cover. There had been one 10years prior, but before the redesign and it was bought it. So this was the first time she has shot & interviewed exclusively. It was also Kristen Stewart's debut British glossy cover. She had only graced the cover of Dazed before this, not a big commercial fashion magazine.
And you're right, Scarlett has not shot for British ELLE previously.