I will become the beast's ex wife

The protagonist finds herself reincarnated/possessed into a 19+ romance-fantasy novel titled "Beauty and the Night Beast". She wakes up as Bella, the younger sister of the first wife who ends up giving the beast trauma. To avoid a doomed fate when her older sister runs off, she voluntarily takes her sister's place to marry the beast with the ultimate goal of safely divorcing him and living a wealthy, independent life.