The conversation in CH:42 is particularly funny as she is in conversation with Mr Knightley regarding the party.

What a contrast.His blunt remarks and her understanding of them.
Her suggestion of coming on a donkey, and his straight face in listening to it, even advising her to borrow one from Mr Coles.

And she leaves with the grand feeling of;
"You have hit upon the very thing to please me."

And the author's comment about her;
"Cabbage beds would have been enough to tempt the lady, who only wanted to be going somewhere."