Rosanna is the one who been to the boudoir at midnight? Why should she went the the boudoir at that time, anything related to the Moonstone?

The scary quicksand, this time devours Rosanna.

Truth is obviously an important theme in a detective novel. Collins lays the metaphor thick here with the quicksand, conjuring imagery of truth lost in the muddy sands. Rosanna also mentions that she "may own" the truth - but is truth not objective fact? It emphasizes the question of perception versus reality and the epistemology of truth. For Rosanna, truth is what she believed to be true, her truth. She died due to the burden of this truth, fully believing in its validity.

This passage highlights the subjectivity in these narratives as a whole. Franklin believes that everyone would interpret Lucy's actions as that of a madwoman, and it is certainly the case that those whom he surrounds himself with would agree. However, there is a perfectly reasonable explanation for Lucy's actions that only women of her and Rosanna's class would know - people who have no voice in these narratives.

Well, at least he's honest about that. it's incredible to me how self-centered Mr. Franklin could be. Up to that point, he barely even recognizes the excruciating pain she must've endured, being treated as non-existent by him; he doesn't exhibit any empathy or sympathy (which is hilarious given that he's chasing Rachel so desperately), as if it is so inexplicable and absurd that she's had feelings for a person so above her societal rank, that it can simply be disregarded. Notice how the entire time he's reading the letter, all he cares about is finding a clue for the Moonstone, or his own ostensible guilt.

However, he's surely endeavoring to justify himself here, not to be seen to the reader as a supercilious, ill-mannered man!

I wonder if Franklin has something to do with Rosanna’s suicide.

This has been mentioned repeatedly by Cuff at this point. Roses have classically been used as a symbol of nobility in England. "Budding" may refer to the mingling or mixing between two different classes of people. If we understand Cuff's words through this interpretation, he is arguing for the "purity" of nobility, or strict adherence to class stratification.

Rosanna's name can also be construed as a reference to the roses in Cuff's argument. By "budding" with nobility, Rosanna has become entangled in an unfortunate event for which she would have been "all the better for not" being involved at all.

It's interesting to see that Betteredge's infinite confidence and sense of "what you see is all there is" when it comes to household matters forbid him from developing any suspicion. Upon reading this hasty refutation, I found myself very discontented with the lack of any additional information to support it -- not even a naive exhibition of blind trust in her, let alone factual evidence that displays the impossibility of this event.

Even if he's right and she is to be trusted, I'm starting to feel that his complacency allows things to slip under his nose without his knowing.

The capitalization of "Person" along with "Thing" leads me to believe that Rosanna may be a key character, especially as Betteredge describes her in great detail compared to the other characters he has introduced thus far. It's interesting that he quips it is "common politeness" to "put the Person before the Thing", when looking at the narrative as a whole, it is the "Thing" which comes before all else. This juxtaposition sets up a dichotomy of the personal versus the objective, which given the format of multiple narrators makes sense.

Also establishes Betteredge as someone who values social etiquette while subtly hinting that those who are obsessed with the Diamond are somehow indecent. Could that be a jab at the audience as well?