I wonder why Mrs. Bennet thought it was necessary to bring Kitty and Lydia with her when summoned by Lizzy to come and see Jane. And what about Lydia charging Mr. Bingley to keep his promise to hold a ball there, and telling him it will be quite a shame if he doesn't? She's only 15 years old and she barely knows him! Isn't it a breach of etiquette for her to speak to him at all?