Charlotte may well have agreed with her husband, although I think she'd draw the line at suggesting Lydia would be better off dead. While I really doubt that Charlotte would speak about the Bennet family's shortcomings to Lady Catherine -- especially since Charlotte would like Lizzy and Darcy to get married -- it isn't hard to imagine her telling Mr. Collins that Lydia was allowed to run wild and that Lizzy and Jane were always trying to put a stop to it. It's the sort of thing a wife might discuss with her husband. Of course, saying it to Mr. Collins is the same as saying it to Lady Catherine.