There don't seem to be any other women in their late twenties in the neighbourhood, so perhaps Jane and Elizabeth are the closest Charlotte has to a contemporary.

And think of the situation in the Bennet household ten or fifteen years ago. Mrs. Bennet has had five babies in quick succession and the older two need more attention than she can give (Elizabeth especially might have been a handful). Practical, levelheaded Charlotte would have been a perfect older-sister figure for them. And on her side, well would you rather spend time in the Lucas household or with Jane and Elizabeth?