"What can be the meaning of this?" said Charlotte, as soon as he was gone. "My dear Eliza, he must be in love with you, or he would never have called on us in this familiar way."

Charlotte is first to suggest that Darcy might have feelings for Elizabeth.

But when Elizabeth told of his silence, it did not seem very likely, even to Charlotte's wishes, to be the case;

I think Charlotte would have been very interested the conversation that really passed between D&E (marriage and family togetherness--in the physical sense of the word.) She is only told of Darcy's silence. Still she becomes watchful of Darcy.

Colonel Fitzwilliam's occasionally laughing at his stupidity proved that he was generally different, which her own knowledge of him could not have told her; and as she would have liked to believe this change the effect of love, and the object of that love her friend Eliza, she set herself seriously to work to find it out. She watched him whenever they were at Rosings, and whenever he came to Hunsford; but without much success. He certainly looked at her friend a great deal, but the expression of that look was disputable. It was an earnest, steadfast gaze, but she often doubted whether there were much admiration in it, and sometimes it seemed nothing but absence of mind.

I wonder if Charlotte wishes she could advise him in a similar manner as she did Elizabeth in regards to Jane

"it is sometimes a disadvantage to be so very guarded. If a man conceals his affection with the same skill from the object of it, he may lose the opportunity of fixing her. " paraphrasing Chap 6

Still, Charlotte must sense something, because she was not entirely ready to let the subject go.

She had once or twice suggested to Elizabeth the possibility of his being partial to her, but Elizabeth always laughed at the idea;