The passage where Emma gives Mr. Knightley full credit for being right about Frank Churchill is a favourite Author Austen subtlety of mine.

Emma also questioned Frank Churchill's motives for inaction, and had been reduced to taking the other side of the question when talking with Mr. Knightley, remember? She is really saying that they were both right to have suspicions, but only Emma (and Mrs. Weston, to whom Emma will likely never mention the matter again) would know it. To Mr. Knightley, her new betrothed, she states the flattering opinion that HIS intellect proved out, as if she never would have noticed Frank Churchill's inconsistencies had Mr. Knightley not brought them to her attention!