But Fanny is the problem. I fear that Jane Austen intended us to accept her as an entirely admirable heroine, reliably virtuous in all her thoughts and judgements. Unfortunately, modern readers do not see her like that. So I hope I am wrong and that really Jane had some 'dark' intention that she nowhere makes explicit.
Fanny's strength is the strength of the anchor. She is firm and steadfast. The others cling to her because she represents the only thing that is certain and secure. But anchors are boring - heavy, unmoving - even though they are needed in a world such as that of Mansfield Park, where people and events change and whirl in a confusing maelstrom.