In chapter 54 Mrs Bennet tells us: "I do think Mrs Long is as good a creature as ever lived - and her nieces are very pretty behaved girls, and not at all handsome: I like them prodigiously."

What a difference from her opinion in chapter 2: "I do not believe Mrs Long will do any such thing. She has two nieces of her own. She is a selfish, hypocritical woman, and I have no opinoin of her"
Mrs Bennets opinions are always dependent on the latest flattery or imagined insult. Before the Meryton Assembly she thinks of Mrs Longs nieces as potentially set up as rivals to her daughters but that they really canīt compete with the looks of the Bennet girls. (Why else would Mrs Long avoid to introduce them as she promised?) Here we learn that Mrs Bennet do not think them handsome at all and how much she likes them because of this. Or maybe it is only because she sees Mr Bingleys attentions are so undividedly given to Jane.