In response to Penny Klein, Dorothy Gannon wrote:
"I'm not quite sure I believe Mary is good to Fanny from such completely ulterior motives as you describe, but I do see a cool bitterness in her which does not seem present in Henry Crawford."
I'd like to agree with Dorothy that in this scene Mary acts out of a group of emotions which are not selfish, have no calculation of gain in them. She is "astonished" by Mrs Norris' cruelty, and her seething public humiliation of Fanny. Her movement towards Fanny is described by the narrator as "almost purely governed" by "really good feelings." It is a spontaneous impulse to soothe, and she says things are getting too unpleasant among them even for her. Austen's words suggest she is embarrassed literally to be placed and metaphorically to find herself on the side of those who "belong" there as opposed to Fanny who is there on sufferance. She moves away from the others, and towards Fanny. Fanny too feels Miss Crawford's act is "kindness."
What always strikes me about this scene though is Miss Crawford's power. Miss Crawford need only throw "a look" at her brother, and he quiets. Later in the book Fanny throws Crawford many a look, and it does her no good at all.
I'd like also to agree that it seems to me that later in the book Henry Crawford emerges as less calculating and mercenary than his sister. It's not just that he asks to marry a girl with nothing and no status, and that Mary is turned toward Edmund once again because she has heard that Edmund may after all be the oldest son. The kinds of language and gestures Henry is given in Portsmouth which are more purely enigmatic or, to put it another way, can have no construction but that he is in love, being kind, tactful, wants to become a good landlord; Mary's behavior in her closing scene with Edmund is somewhat enigmatic and she may speak sharply because he makes her uncomfortable, but her behavior and words also show her to be cold, lack feeling (towards Maria and Henry now and if they had not run off and Henry had married Fanny towards Fanny--yearly flirtations indeed), and we are not left to construe her last appearance in front of Edmund as a poignant appeal, but rather another attempt to conquer him sexually: "it was a smile ill-suited to the conversation that had passed, a saucy playful smile seeming to invite in order to subdue" (Chapman III:16, 459).