Her goal wasn't to take revengeon the first place. The FL/ demon just want to experience the human world but since she made a contract with Marraine it leaves her no choice but to comply the contract.
I don't know if I remember it right but Marriane (og) didn't get to say what she wish for when they made a contract
she did but the demon forgot to ask for payment
Nvm I read it again and I remembered it wrong sorry bout that. Yurisina (FL) forgot to ask for payment not the wish
i don’t know what’s the plot anymore. at first, she took over the body in exchange for the og’s soul because the og wanted revenge and all but she’s not even doing it quite actively. i don’t know the direction of the story anymore.