I agree there is more to Charlotte than what might first meet the eye.

"To oblige you, I would try to believe almost anything, but no one else could be benefited by such a belief as this; for were I persuaded that Charlotte had any regard for him, I should only think worse of her understanding than I now do of her heart. My dear Jane, Mr. Collins is a conceited, pompous, narrow-minded, silly man: you know he is, as well as I do; and you must feel, as well as I do, that the woman who marries him cannot have a proper way of thinking. You shall not defend her, though it is Charlotte Lucas. You shall not, for the sake of one individual, change the meaning of principle and integrity, nor endeavour to persuade yourself or me that selfishness is prudence, and insensibility of danger security for happiness." (Chapter 24)

Can you say what she does that you find shocking. Is it that she had a scheme—that she manipulates Mr. Collins into marrying her? Do you mean shocking as in disapproval or or just surprise? In what way are Charlotte’s activities selfish? Lizzy has been grateful for Charlotte’s good-natured relief in engaging Mr. Collins conservation and attentions to herself since Chapter 18 but is rather put out when she learns it has resulted in an engagement. I think Lizzy is quite shocked at Charlotte’s acceptance of him but is also disappointed and disapproves that her friend would marry a man she does not love for security—not only that but a stupid man, one well below her own abilities. Lizzy thinks Charlotte is acting selfishly but I do not.

Sir William and Lady Lucas were speedily applied to for their consent; and it was bestowed with a most joyful alacrity. Mr. Collins's present circumstances made it a most eligible match for their daughter, to whom they could give little fortune; and his prospects of future wealth were exceedingly fair. Lady Lucas began directly to calculate, with more interest than the matter had ever excited before, how many years longer Mr. Bennet was likely to live; and Sir William gave it as his decided opinion that, whenever Mr. Collins should be in possession of the Longbourn estate, it would be highly expedient that both he and his wife should make their appearance at St. James's. The whole family, in short, were properly overjoyed on the occasion. The younger girls formed hopes of coming out a year or two sooner than they might otherwise have done; and the boys were relieved from their apprehension of Charlotte's dying an old maid. (Chapter 22)