Elinor's narration to Marianne contained "all the comfort that could be given by assurances of her own composure of mind, and a very earnest vindication of Edward from every charge but of imprudence, was readily offered".

Marianne believes that Edward was not vindicated, and if Elinor really "had loved him most sincerely" then Marianne doesn't believe that Elinor could feel less than she (Marianne) felt when Willoughby's true situation/nature was revealed. Marianne did not believe Elinor's "assuranne of her own composure."