Yes, I was also surprised by the fresh outbreak of callousness. Her behaviour had been tending the other way: she'd been gracious toward Edmund in ch34 with a look of satisfaction, and words of simple, pleasant meaning.

Finally, when I was about ready to give her up as a bad job, the narrator regathered my sympathy for her by showing that some good influence did eventually sink in (ch48): ...Mary ... was long in finding ... any one who could satisfy the better taste she had acquired at Mansfield, whose character and manners could authorise a hope of the domestic happiness she had there learned to estimate, or put Edmund Bertram sufficiently out of her head.