...Austen was living through the rise of the Romantic period in the arts, and she was very distrustful, even disdainful, of much of the excess that characterized that period. I think that even in this, her first work (though not the first published), she was already reacting.

Consider that Charlotte is 7 years older than Lizzy; she's plain; she's already considered destined to be an old maid; she's likely to be as poor as Lizzy will be as soon as Mr. Bennet dies; there are few or no eligible bachelors in the neighborhood for either of them; her father is just as irresponsible as Mr. Bennet in refusing to travel to a place where they might find husbands; Charlotte's brother(s?) are much younger, and already chafing at the prospect of having to support her.

Charlotte, like Collins, has been unbelievably lucky! Of course she did the right thing.