I think Fanny is keenly observant and fairly courageous in accepting how things are rather than seeing them through rose-colored glasses. She relies on her principles to guide her own behavior and when judging other people. It particularly shows when she feels she is being unfair to someone else, usually Mary and she recommits herself to trying to be fair. She is also incredibly empathic which makes her extraordinarily kind to others. I do not suppose this is all that makes Fanny wise, for she certainly is more so than those around her, but it is all I can think of at the moment. (:D)