On a related note, after considering the Ms. X situation some more, I'm firmly of the opinion it's some combination of Moira/Jessica. On a narrative level, I just can't see it being any of the main LIs, which eliminates all of the other decent candidates who have only one reason why they "can't" be the blackmailer (IMV these are Delilah, Bella, Evelyn, Oriana, and Natasha). With them excluded, Moira/Jessica has the most means and motive, not to mention reason to single out Vanessa in some tasks.
Why is this related? Because at this point, the most likely person to discover this is...Vanessa. And that would set up a damn fine redemption arc.