The remark in chap 53 implies that Emma was already thinking of a possible future match between one of her nephews and Mrs Weston's daughter! But JA didn't disapprove of thinking of possible matches, what was disapproved of was active interference and scheming -- which was what Emma did in her attempts to match-make Harriet and Elton. (And which matchmaking mothers e.g. Mrs Bennet would do in their efforts to matchmake their daughters).