each time I see this pop up, I confuse it with another manga (which ends up making me very confused as I read this) which I am more curious about, but have somehow misplaced somewhere in my memory.
Anyone remember the name of the one where a girl has reincarnated as a dukes daughter and transformed her territory into a super isolationist region with everything from trains to guns, and the story is about how some prince gets married to her as a form of exile, and is very surprised at what he ends up seeing there? There is also some form of subplot about her being a fujoshi and forcing her new husband to have sex with his bodyguard against his will (which is why I confuse those two).
edit: found it! it was Daites Ryou Koubouki