She is even telling Jane and Elizabeth how they are the objects of gossip - and not necessarily nice gossip. Lydia lacks tact even within her own family! And notice how deprecatingly she speaks of the 'formality and discretion' of her two most respectable family members!

By the way, who says the line "She is a great fool for going away, if she liked him." ? It sounds like one of the three younger girls, but I can not decide which. In P&P2, they give a softened variation of the line to Maria, but Maria is not usually so flatly condemnatory. Maybe Lydia is a bad influence on HER, too!