An ironically named character if there ever was one, this lady is always either seated or cruising around in her fancy carriage giving out condescending looks left and right like they were event fliers.
Mrs. Walker is like Mrs. Costello, Jr. She, too, is scandalized by Daisy's behavior. Unlike Mrs. Costello, who seems to get most of her social power by refusing visits and making herself scarce, Walker's a bit of a social butterfly, hosting a lot of get-togethers in Rome.
Her children are at school in Geneva, and it's from spending winters there that Walker and Winterbourne became tight. We never see nor hear anything about Mrs. Walker's husband, which is a little suspicious if you ask us. Did James mean to imply there's a little behind-the-scenes action between Walker and Winterbourne? It's not out of the question but it's not exactly in the story either.