...you could also make a case that she's contradicting herself twice in your example, because she says that doesn't like to boast of her own daughter's beauty when she is actually doing just that! ;-) There is also this passage from Chapter 2, in which Mrs. B manages to contradict herself within one sentence(emphasis mine) :

"I do not believe Mrs. Long will do any such thing. She has two neices of her own. She is a selfish, hypocritical woman, and I have no opinion of her."

See what I mean? It seems that she does have an opinion of Mrs. Long as she's just expressed it! ;-) One also might wonder how well she can stand up to her own criticism. We find out that Mrs. Long wouldn't yet know Bingley by the time of the Assembly. Would Mrs. B go out of her way to introduce Mrs. L to the young man, or would Mrs. Long's nieces have to depend upon the kindness of Lady Lucas for this favor? ;-)