In Pygmalion Clara and Eliza approach presenting themselves with the appearance of being ladies from two vastly different frames of reference. Clara, though not of the highest social circles herself due to her mother's sorely limited income, associates with those circles. Eliza, by contrast, prior to her contact with Higgins, has never had any contact at all with better social classes except to try to sell them flowers on the street corner. This means that when Clara tries to present herself as a lady at a social event like Mrs. Higgins' at-home she can well do it, within the limits of her personality, temperament and education.
When Eliza tries to present herself as a lady (at this early stage of her training) she comes at it with misconceptions, limits on comprehension, ignorance of form and subtleties of manner and cannot well do it: She can dress the part and appear the part because of her beauty and to some extent act the part because she can learn to pour tea from a teapot but cannot think the part or speak the part. Though Clara has her own problems with social grace, courtesy of manner, consideration and intelligence, she and Eliza are still worlds apart in the attempt to present themselves as ladies. In the end though, when Eliza's natural good-heartedness combines with the linguistic and social cultivation Higgins has bred in her, she obviously surpasses the gruff, unpleasant, ill-mannered Clara in presenting herself as a lady.