Charlotte's not a burden to her family. In fact, she seems to be a big help, as the eldest of a large clan. We're told she helps out in the kitchen, and I'm sure she's had a hand in helping to care for her younger siblings. But we're told that her parents don't have much fortune to leave her, so if she stays unmarried she will have to live with a brother or married sister. Mr. Collins' offer is a most eligible one for her. And as for letting her go, she is 27 years old, an age at which most women at the time were married. And eventually, she may be their neighbor, after the decease of Mr. Bennet. So there is much for the family to be happy about.