I think the change you are referring to centers around Elizabeth. Elizabeth is a proud character and the ball exposed her family as lacking. This mortifies her.
The Bingleys go to winter in London, while there Miss Bingley sends Jane a letter insinuating that Bingley himself may become engaged to Darcy's sister. Jane is hurt and Elizabeth feels this pain for her sister. Obviously someone has convinced Bingley that Jane isn't a good match, nor is she interested in him. Elizabeth leaves the chapter infuriated at this manipulated communication.