I think Mary knew what she was doing when she ‘spoke of ‘Fanny,’ and spoke of her as a sister should’ (40) and she did it specifically to observe how Mrs. Rushworth would react. Maria’s loss of composure is amusing to Mary and she does indeed enjoy telling Fanny about it. Mary knew both the Miss Bertrams were in love with Henry and it especially got the better of the elder. I feel Mary is contemptuous of Maria for falling for Henry’s tricks, perhaps also for letting a man steal her tranquility.

One reason I feel Mary was purposeful is that she goes on to arrange something worse for Mrs. Rushworth by persuading Henry to attend Mrs. Frasier’s party to meet with her, or rather taunt her with his presence. As she wrote Fanny: He will see the Rushworths, which own I am not sorry for—having a little curiosity, and so I think has he—though he will not acknowledge it” (43). Fanny has no good opinion of Mary’s intrigue and credits Henry for his lack of interest:

‘That Miss Crawford should endeavour to secure a meeting between him and Mrs. Rushworth, was all in her worst line of conduct, and grossly unkind and ill–judged; but she hoped he would not be actuated by any such degrading curiosity. He acknowledged no such inducement, and his sister ought to have given him credit for better feelings than her own.’ (43)

I guess this is not teasing Mrs. Rushworth with Fanny’s name but it is all in all much worse not only for her but also for Mary and Henry. Edmund’s account of their meeting at the party was “they did not meet as friends. There was marked coolness on her side. They scarcely spoke. I saw him draw back surprised” but Mary was not surprised. Mary really is a mean girl and I have a little pity for Mrs. Rushworth because although she is vain and selfish she does not deserve to be selected for so much torment.