I thought she was referring to Harriet's sore throat, not that she knew about Harriet's hopes. I don't think anyone know about Harriet and Elton, other than Harriet, Elton, Emma and Mr Knightley.

This is one of my favourite chapters as well. Miss Bates is delightful jumping from pork to marriage to Mr John Knightley to her mother's deafness etc.

Also, this bit always makes me smile:
"'A new neighbour for us all, Miss Woodhouse!' said Miss Bates joyfully; 'my mother is so pleased! she says she cannot bear to have the poor old Vicarage without a misstress. This is great news, indeed. Jane, you have never seen Mr Elton; no wonder that you have such a curiosity to see him.'
Jane's curiosity did not appear of that absorbing nature as wholly to occupy her." (21)