Duchess in the Attic(2018)

Yane Urabeya no Koushaku Fujin

Opal Holloway is a determined young lady whose ambition makes her stand out among her peers. When her entire life is seemingly changed overnight, she's left without a man to marry. However, she couldn't be more relieved, since she's been secretly in love with her childhood friend Claude. Opal hoped that she wouldn't be forced to marry a noble other than her childhood friend, but bad news arrives. Wed to a childish duke, whose servants refuse to treat her well, Opal feels like the whole world has turned against her.

But Opal isn't one to take things lying down. She decides to use her wealth to steal Duke McLeod's land and manor away! Now in charge, will she be able to transform the servants and the duke? And will she ever be able to forget her first love?

(Source: J-Novel Club)