For a start, the pain associated with Mr Price looks to me like the pain of disappointment. Fanny goes on to reflect a few paragraphs later: She was at home. But, alas! it was not such a home, she had not such a welcome, as—she checked herself; she was unreasonable. What right had she to be of importance to her family?

This sort of reflection, or self-examination, is a recurring theme. (I know I've posted recurringly about it.) Firstly Fanny goes and thinks an unguarded thought -- sometimes quite an extreme one -- but then she turns it over in her mind, judges it with as much rational candour as she can muster, and discards it. (Mary Crawford in the same situation would be more likely to polish it up and blurt it out.)

Could that be something to do with the ambiguity you're talking about? That is, the difference between Fanny's spontaneous thoughts and reflective thoughts?

I'm inclined to describe her journey as a scramble into maturity and toward self-assurance. She's in stark contrast to JA's two previously-published heroines, the iron-willed Elinor Dashwood and Elizabeth Bennet. It's a huge red-letter day when she withstands the pressure to marry Mr Crawford.

What with trying to cope with her spontaneous thoughts, and not being so self-assured, she's more reminiscent of Catherine Morland. Remember that a forerunner to Northanger Abbey was sold to a publisher in 1803, and bought back in 1816. By the time JA was writing Mansfield Park, I think it was reasonable for her to recycle some ideas from the mysteriously unpublished manuscript. (Another NA-ism in MP is when Sir Thomas wished Mr Crawford to be a model of constancy; and fancied the best means of effecting it would be by not trying him too long (ch35), which reminds me very much of Mr Tilney's "Or is her heart constant to him only when unsolicited by anyone else?" in NA ch19.)