I wrote it in another message as a clarification but would JA have mentioned Charlotte helping Elizabeth at the ball if it weren't to plant the seed of thought in our minds so when they are engaged we say "Oh, well maybe that’s where Charlotte began her growing esteem for Mr. Collins" Whether it was her intention or not that is where they begin to get to know each other better! Is it such a stretch to think that an unmarried women would share an evening with a man, and not think "what if" Not much is said on that and I might be pushing thoughts into the characters head but I fully believe JA would not mention their involvement at the ball if it weren't to infer some intentions growing.