I used to work at Burberry Prorsum and had exclusive access to this Spring/Summer's collection last Spring/Summer, a year in advance. Well, I was told that one of the main reasons why Agyness Deyn was being scaled down as a model for Burberry, was because they were embracing a more feminine look (whcih Rosie Huntington Whitely had) and which Agyness Deyn didn't. So it is not surprising to see her looking more feminine here, at the Met Ball, as I think this has been stipulated in her contract. That is why she has been letting her hair grow etc.
Sukoesuki