I think this reason has been suggested but the novelty of the visitors has not worn off yet for this bored old woman. Reading over the text she seemed out of sorts that evening (upset to see Lizzy and Maria leave? ;)) Her nephews had just left, now these two young women were escaping her domain. Fewer people to pontificate over. As for her point about daughters not being of much consequence to their fathers, the rude old bat is just trying to find an excuse to make them stay on because the two months aren't up and she's in the doldrums. As for Anne's relationship with Sir Lewis, I'm unsure if he knew his daughter well. Maybe one or both parents were disappointed she was not a boy to carry on the family name. If Anne was a sickly baby, her father may have also felt this did not ensure security for the family line.With the appearance of no other children, perhaps that's when Lady C. began making her plans to secure the family line and estates.