[HELP FIND SOURCE]

So the MC is reincarnated as the villainess, she used to be engaged with the crown prince but she dabbled in dark magic so she got put on house arrest at a dark haired dukes home and she is acting unlike herself, the Mc also has a brother who was adopted from a collateral line of relatives and she has purifying magic I believe, her brother has this weird little fairy cat that makes him not a wizard but a contractor and the OGFL is like actually evil. The mc was put jnder house arrest after being suspected of stealing a national treasury book, I CANNOT REMEMBER THE NAME OF IT PLS HELP