After re-reading the passage, I see your point. Even if a woman was expected only to sew, play music, and so on, it would appear that Mr. Bennet didn't see to this as well as he should have. Elizabeth admits that none of the girls can draw, and only one plays and sings. Though, they all can sew. Perhaps Lizzy should be a bit more embarrassed about her parent's neglect, but maybe Lady Catherine's overly high expectations are a bit ridiculous as well.