Two inferences, however, were plainly deduced from the whole; one, that Elizabeth was the real cause of all the mischief; and the other, that she herself had been barbarously used by them all; and on these two points she principally dwelt during the rest of the day.

Mrs Bennet is having a very bad time of it.

First, Elizabeth refuses to marry Mr. Collins. Then it turns out that Charlotte Lucas is to marry him instead, which left her "too much overpowered [by the news] to say a great deal while Sir William remained", a rare occassion for Mrs. B.

Lady Lucas can't help but rub it in.

Lady Lucas could not be insensible of triumph on being able to retort on Mrs. Bennet the comfort of having a daughter well married; and she called at Longbourn rather oftener than usual to say how happy she was, though Mrs. Bennet's sour looks and ill-natured remarks might have been enough to drive happiness away.

But can we blame Lady Lucas? Remember what she had to endure at the Netherfield ball?

[Mrs. B] was talking to that one person (Lady Lucas) freely, openly, and of nothing else but of her expectation that Jane would be soon married to Mr. Bingley. -- It was an animating subject, and Mrs. Bennet seemed incapable of fatigue while enumerating the advantages of the match. Ch.18

And Lady Lucas is not the only talking of the match.

The very mention of anything concerning the match threw her into an agony of ill-humour, and wherever she went she was sure of hearing it talked of.

But the village gossip is no solely dealing with Charlotte's engagement, for Mrs. Bennet must also hear about Mr. Bingley.

Day after day passed away without bringing any other tidings of him than the report which shortly prevailed in Meryton of his coming no more to Netherfield the whole winter; a report which highly incensed Mrs. Bennet, and which she never failed to contradict as a most scandalous falsehood.

Is it any wonder that "Mrs. Bennet was really in a most pitiable state"?