Tigerlily

That could be! I don't find her unrealistic, but apart from her role as plot-mover and abuser of Fanny, she just seems to be there. She really doesn't have anything to do but try to control her social environment - and now that you mention it, she also seems to reject living one traditionally feminine role that requires commitment: motherhood. Granted, she makes sure to mind the business of the Bertram children, especially the daughters, and to influence what happens to Fanny, but she doesn't take direct charge of any of them and finds ways to reject having to raise Fanny herself. Mrs. Norris learned to use soft power, and had to get married if only for the status of it (probably) but she never wanted any more feminine responsibility than the minimum of what was respectable. She was just less languid and more dominating than Lady Bertram.