] True, but she has been so self absorbed and trampling so hard on everyones feelings by this point, that I find it impossible to give her the benefit of the doubt.

Yes, she is self absorbed, but but she doesn´t, IMO, understand that she hurts others as much as she does. It´s not her intentions to do so anyway. That is an important difference between her and Fanny or Lucy. Marianne has the ability to mature, which I doubt either Fanny or Lucy have.

] True, but a clever person is capable of analyzing things and seeing meanings that others don't see. Once the evidence was there that Willoughby was not the man he presented himself to be, she would have figured it out if she were truly clever. She has still yet to prove the narrator's description as true with either her actions or words.

I´m not sure I agree with your definition of being clever. And why Marianne at first doesn´t want to see Willoughby as he is, I think that Line has explained that very well in her post "True Love" just below. :-)