for self-deception. She is at present telling herself she is a little bit in love with Frank Churchill and he is even more in love with her. As her internal rant concludes she thinks "Oh! what would Frank Churchill say to her, if he were here? How angry and how diverted he would be! Ah! there I am thinking of him directly. Always the first person to be thought of! How I catch myself out! Frank Churchill comes as regularly into my mind!"

Frank Churchill was in fact the fourth person she thought of, after Mr Knightley, Mrs Weston and Harriet in the passage you quoted. I don't think she is in love at all - a woman who is does not conjure up scenarios of refusing the man in question then passing him on to her friend. I'm not sure if he is either.