] The fact that she has not, leads to the confusion, for her actions with him are of such an intimate nature, actions one would not engage in if one were not engaged. But, why not just ask her? They are sisters, confidants...

Having a sister whose outlook on life sometimes differs from mine, I can understand Elinor's predicament a little bit, especially when our relationship was more volatile. If we didn't receive a confidence from the other, we didn't ask, since this would be seen as some sort of breach of privacy or trust. I can see this being true with Marianne, too, esp. as Elinor observes, "from you, her mother...the question could not give offence" (Ch. 16)