Emma's trying to control a situation that is rather out of her sphere of influence. She can't control the Martins' behavior, and they have this annoying tendency to behave like real people instead of pieces on Emma's chessboard. (How dare they!)

Emma has pretty good luck controlling many people's behavior. For various reasons, she can act as mistress of Highbury and direct many comings and goings.

But the Martins and Jane Fairfax simply refuse to bow to her will. Emma cannot forgive Jane for not being the unreserved person Emma wants her to be. And she finds the Martins hard to manage because they won't behave the way she'd like: they are too good and genteel to stop talking to Harriet or be less than open and welcoming to her. They won't go in the pidgeon hole she has prepared for them (that is, they won't simply be beneath her notice and therefore invisible) Instead, they are worthy people.

Emma finds it hard to let most people be themselves. She wants to reinvent them to fit the place her in life they are supposed to fit. If they're willing to go where they're told, she's very happy to know them. If they won't, she isn't happy to know them.

But I sincerely believe that she is unaware that she's doing this to people. She's a master at rationalizing. She quite honestly believes that she sees things clearly, and the way they should be seen.