The answer is: Mrs. Merriweather is being a hypocrite.
In Harper Lee's "To Kill a Mockingbird," Mrs. Merriweather is criticizes Atticus because of his defense of Tom Robinson. Therefore, Miss Maudie silences her and exposes her hypocrisy, as well as that of the other ladies at the fund-raising event who have Mrs Merriweather's ignorant thoughts.