Emma admits to herself the Martins have every right to feel resentful after Harriet’s insultingly short visit to them in Chapter 23, “Emma could not but picture it all, and feel how justly they might resent, how naturally Harriet must suffer.” I think the Martins know to whom Harriet’s change of manners towards them can be attributed although I do not recall any active resentment on their part. Harriet is too enthralled by Emma to feel any resentment for what her mentor’s snobbery has done for her. Emma neglects Jane Fairfax and the Bates although they do not seem to resent it. The only persons who have retaliated against Emma (though Harriet mostly) is the Eltons and even they have middling-fair resentment against her.

In one respect Mrs. Elton grew even worse than she had appeared at first. Her feelings altered towards Emma. Offended, probably, by the little encouragement which her proposals of intimacy met with, she drew back in her turn and gradually became much more cold and distant; and though the effect was agreeable, the ill-will which produced it was necessarily increasing Emma's dislike. Her manners too -- and Mr. Elton's, were unpleasant towards Harriet. They were sneering and negligent. Emma hoped it must rapidly work Harriet's cure; but the sensations which could prompt such behaviour sunk them both very much. It was not to be doubted that poor Harriet's attachment had been an offering to conjugal unreserve, and her own share in the story, under a colouring the least favourable to her and the most soothing to him, had in all likelihood been given also. She was, of course, the object of their joint dislike. When they had nothing else to say, it must be always easy to begin abusing Miss Woodhouse; and the enmity which they dared not shew in open disrespect to her, found a broader vent in contemptuous treatment of Harriet. (Chapter 33)

Emma’s attempt to match Mr. Elton and Harriet was presumptuous and highhanded. She admitted to herself in Chapter 16 she appeared to encourage him, “If she had so misinterpreted his feelings, she had little right to wonder that he, with self-interest to blind him, should have mistaken her’s. Mr. Elton made a fool of himself in the carriage by not immediately accepting rejection but I think it was Emma’s machinations which led them there. Emma disliked Mrs. Elton so much she refused all her offers of intimacy and brought on their resentful behavior towards herself and Harriet. Of course I don’t think Emma should have done everything Mrs. Elton suggested but a little more attention towards her by Emma might have prevented their meanness to Harriet.

Emma has prevented Harriet from accepting a good man in marriage, she has used etiquette to put people in their place and she brought on the Elton’s mean and resentful behavior towards herself and Harriet by neglecting the lady. I don’t think it is far fetched people might not appreciate Emma’s attitude or the treatment they receive from her. I think Rachael G made a valid point.

"It was an awkward business, my dear, your spending the autumn at South End instead of coming here. I never had much opinion of the sea air."

"Mr. Wingfield most strenuously recommended it, sir, or we should not have gone. He recommended it for all the children, but particularly for the weakness in little Bella's throat -- both sea air and bathing."

"Ah, my dear, but Perry had many doubts about the sea doing her any good; and as to myself, I have been long perfectly convinced, though perhaps I never told you so before, that the sea is very rarely of use to any body. I am sure it almost killed me once." (Chapter 12)

I don’t think Mr. Woodhouse’s objection to South End has anything to do with it being less fashionable than somewhere else but rather a lot to do with his not liking sea air and the fact Mr. Perry recommends a different watering place in Chapter 12, “Perry was a week at Cromer once, and he holds it to be the best of all the sea-bathing places.” Mr. Woodhouse and Isabella are having gentle disagreements about whose medicine man is best but to me it has nothing to do with social snobbery.