I don't get the concubine suggestion. Even though she's the daughter of a lower aristocrat, she's still nobility. He's the emperor that just conquered everything so there's no need for a political marriage alliance.
I know she doesn't see him in that way at all though. He's so adorable. Poor guy.
She's an idiot. She knows nothing about the world/society she now lives in.
She's not even trying to learn about the country or political climate that affects their noble house.
Instead she wants the heir of a Duke to behave like a "normal" child from her modern & peaceful life as a daycare...