Emma has long been interested in the idea of Frank Churchill, and she is well aware that there has been speculation about a possible match between them. When Frank finally arrives Emma finds much that she likes, and enjoys his attentions to her. She magnifies small things she approves of (eg Frank's admiration of Mr Elton's house) into larger, much more general good qualities. She also rationalises away her disapproval, for example of Frank's trip to get his hair cut. Emma is very willing to be (almost) fallen in love with, but has no idea of falling in love herself.
Emma's reaction to Frank seems to be superficial. It is like a game, acting out an imagined scenario. I get the impression that she is very detached about him - all in all a very lukewarm response.
In contrast, there is nothing remotely lukewarm in Emma's reaction to Mrs Weston's notion of a match between Mr Knightley and Jane Fairfax - she absolutely HATES the idea! I get the sense that this reaction comes from a much deeper place than her response to Frank - it seems quite visceral. Emma's conscious concern is for little Henry's interests and for John and Isabella, but the strength of her feelings hints that there may be something more going on, and I am not convinced that her dislike of Jane Fairfax has very much to do with it.
Any thoughts?