She had "got" Mary for ever.

She was suddenly conscious that she despised Mary, and had lost all interest in her.

She didn't want the ring, nor did she ever wish to see Mary again.
She gazed about the garden, shrugged her thin, little, bony shoulders as though she were fifty at least, and felt tired and dull, as on the day after a party.

She stood and looked at Mary and her nurse; when she saw them walk away she did not move, but stayed there, staring after them.
She was greatly disappointed; she did not feel any pleasure at having forced Mary to obey her, but would have liked to have smacked and bitten her, could these violent actions have driven her into speech.

In some undetermined way Mary's silence had beaten Sarah.