Other people in this thread have commented on the difference between Emma's attitude to the impoverished cottager and the impoverished Bates. I see a lot of similarities.

When Emma thinks it would be edifying to give Harriet a view of the Highbury parsonage, providentially, a cottager that Emma patronizes, that lives just down the lane from Mr Elton, is very sick. We know that Emma does not know the geography of that part of Highbury very well, and she is a quick study. Could it be that she has never been to this cottage before?
Her benevolence is unstinting, when she does arrive, and in addition to the gratitude she receivers from the cottager, she has a deep sense of her own timely usefulness, that is only reinforced when her ulterior scheme bears fruit. Mr Elton esteems her goodness as highly as she does herself, and invites the girls into the parsonage.

Later, Mr Eltons charms are palling and Emma finds Harriet's conversation tedious. She spys the entrance to the Bates, and decides on the spot that Miss Bates would at least vary the topic and share the tedious burden of conversation with Harriet. Recalling that she does not often call on the Bates, she considers how it would please Mr Knightley to know she did, how it would still her conscience, and (the icing on the cake) how unlikely it is that Jane Fairfax's goodness would have to be endured, before deciding that she is doing a noble deed indeed!
Of course, the Bates are pathetically grateful of the favour, and Emma is splendidly gracious (in spite of the odious Jane Fairfax).