Her attitudes and beliefs up to her snubbing by Willoughby in London, and to some extent thereafter, are all utterly geniune, but nonetheless artificial and contrived for all that. Her opinions only become truly hers towards the end of the book. Of course, in total contrast to Willougby, her performance is purely for her own benefit - she doesn't give two hoots about what other people think of it. (A bit like her "performance" at the piano, really....)

Something of a parallel between Willoughby and Marianne here? At first: duplicity, whether of themselves or others, followed gradually by a process of self-realisation, leading to a decided change for the better in Marianne's case and what could be seen as a change for the worse in Willoughby's. He does not promise Elinor near the end of their interview that he will improve himself - instead he says that he must "rub through the world as well as he can". If you're a villain, is it better knowingly to be one, like Macbeth, or to have convinced yourself that you're not, like - maybe Stalin?