If you ever wondered what 'passive-aggresive' is just watch 'Poor Charlotte' in action. A half century before the invention of the term, Forster did the 'type' to perfection. And the great Maggie Smith brought it to life.
The last scene where Charlotte is reading Lucy's letter, there is a tinge of regret that she was never able to feel the sort of passion that Lucy did. It's rather heartbreaking in a way, because I think like Shirley MacLaine in "Terms of Endearment", the right lover really would bring her back to life, although in the period setting, there is no way that Charlotte would allow herself to be seduced, no matter how much she longed for it deep down.
"Great theater makes you smile. Outstanding theater may make you weep."
She didn't need a lover she needed a loving husband. Those who live alone too long often get too cranky and stuck in their ways to marry anyone however.