Fanny's character development is not as easily noticeable as Elizabeth Bennet's or Emma's, but not all character development has to have lights flashing over it. Through the course of the novel, Fanny becomes a more mature person, and increases in importance in the MP circle.

For instance, as a child, Fanny has a kind of hero-worship of Edmund, but his infatuation with MC makes her realize that he has faults too. Also, when she goes to Portsmouth to visit her family, she has romantic notions of fitting in wonderfully with them and of becoming a close confidant of her mother. But reality strikes a wake-up call and she is forced to change her perspective. But instead of retreating into her shell, as she would have done at MP, she starts mentoring the one person who seems to have the inclination and willingness to listen to her gentle wisdom.

Fanny is not without faults either. She is Mary Crawford's harshest critic. In the end, when Fanny calls her cruel for saying "‘Why would not she have him? It is all her fault. Simple girl! I shall never forgive her. Had she accepted him as she ought, they might now have been on the point of marriage, and Henry would have been too happy and too busy to want any other object. He would have taken no pains to be on terms with Mrs. Rushworth again. It would have all ended in a regular standing flirtation, in yearly meetings at Sotherton and Everingham.’" Ch. 47, it is Edmund who, with his newly opened eyes, is able to judge MC rightly: I do not consider her as meaning to wound my feelings. The evil lies yet deeper: in her total ignorance, unsuspiciousness of there being such feelings.

Finally, not only does Fanny elevate Edmund by accepting him, he elevates her by marrying her. Her transition from poor dependent cousin, to a true daughter of the family, is thereby, complete. In marrying Edmund, she gains a husband who will truly respect and cherish her, and who will not startle her gentle sensibilities by anything rash or vulgar.

The religious themes in MP are certainly more apparent then in Austen's other novels, and one has to take them into account to have a full understanding of MP, but I cannot see any evidence that ordination was meant to be its central theme. We do not even see a description of Edmund's ordination, and it is mainly used to begin revealing the incompatibility between MC and Edmund.

That infamous line to Cassandra where Jane says "Now I will try to write of something else; – it shall be a complete change of subject – Ordination" was written when Jane was well into writing MP and is squeezed between some inquiries Jane asked Cassandra to make for her regarding hedgerows.

Here's the relevant part: "As have not a great deal of Ingenuity themselves."—The 2d vol. is shorter than I cd wish—but the difference is not so much in reality as in look, there being a larger proportion of Narrative in that part. I have lopt & cropt so successfully however that I imagine it must be rather shorter than S. & S. altogether.—Now I will try to write of something else;—it shall be a complete change of subject—Ordination. I am glad to find your enquiries have ended so well.—If you cd discover whether Northamptonshire is a Country of Hedgerows, I shd be glad again.—We admire your Charades excessively, but as yet have guessed only the 1st. The others seem very difficult. There is so much beauty in the Versification however, that the finding them out is but a secondary pleasure.—" Jan 29, 1813