I think a lot of us assume that Charlotte is more desperate to marry than Lizzy, because she is 7 years older. I have been kind of taking that view for granted. But as I wrote another post, I realized that in some ways, Lizzy is actually in a more dire situation.

Lizzy has four unmarried sisters, none of whom has a significant dowry. Their father's estate is entailed away. The fate of all five sisters, plus their mother, is at stake when they decide to accept or reject a proposal.

Charlotte, on the other hand, has a father who had made a tolerable fortune (Ch. 5). We don't know how it is to be split up among his children, but Charlotte might have more than the Bennet girls. It's true, the Lucas's had several children, but this is not necessarily negative either. We know that some of them were boys. Although the text does not say, I would imagine the boys either are learning a trade, or Sir William has enough money that his sons too can be gentlemen. The worst-case scenario I see for Charlotte is living with her aging parents or a sibling's family. Her chances of being poor, like Miss Bates, are almost nil.

The Bennet girls have no one to support them after their father dies. If at least one of them does not marry "well", they will sink lower. I know it has been discussed on Austenuations before whether they would be better or worse off than the Dashwoods of S&S. But my point here is that they would almost certainly be worse off without such a match than Charlotte would. Her position in society is much more secure. She has only herself to please. Lizzy must think of how refusing Mr. Collins might affect her mother and sisters as well.