All quotes from Chapter 10:

Though now the middle of December, there had yet been no weather to prevent the young ladies from tolerably regular exercise; and on the morrow, Emma had a charitable visit to pay to a poor sick family, who lived a little way out of Highbury.

"I do not often walk this way now," said Emma, as they proceeded, "but then there will be an inducement, and I shall gradually get intimately acquainted with all the hedges, gates, pools, and pollards of this part of Highbury."

Good catch! (;D) I think it is likely Emma does not visit the vicarage so she has probably walked to the cottage before but as she says not often and I think the idea that when Harriet becomes mistress of the vicarage she will then get to know the area intimately shows that Emma really does not come this way often for charity or otherwise. Perhaps these cottagers do not often become ill or need the help of their lady patroness? Perhaps Emma has some charitable work at other cottages? I think it does raise questions that Emma does not know these cottagers particularly well, all their ways or otherwise. LOL!

They did as they were desired; and by the time she judged it reasonable to have done with her boot, she had the comfort of further delay in her power, being overtaken by a child from the cottage, setting out, according to orders, with her pitcher, to fetch broth from Hartfield. To walk by the side of this child, and talk to and question her, was the most natural thing in the world, or would have been the most natural, had she been acting just then without design; and by this means the others were still able to keep ahead, without any obligation of waiting for her. She gained on them, however, involuntarily; the child's pace was quick, and theirs rather slow; (Chapter 10)