Dorothy has a younger sister, Beatrice, after whom Beezus is named. Beezus and Ramona firmly believe that Dorothy and Beatrice had always gotten along famously, but the girls are shocked when Dorothy and Beatrice admit that, when they were children, their relationship was, at times, as contentious as Beezus and Ramona's; Dorothy cites a particular incident in which Beatrice, jealous that Dorothy had acquired an autograph book, proceeded to sign her name in multiple permutations on every page of the book. Beatrice would not talk to Dorothy since the revenge but eventually they made up when their mother gave them both new autograph albums for Christmas. Dorothy was described as the more sensible of the two sisters, while Beatrice grew up quite hasty.
Mrs. Quimby is played by Lynda Mason Green in the 1988 television series Ramona, and by Bridget Moynahan in the 2010 film Ramona and Beezus.