She was killed in her first life with no investigation. The powerful mage who gave her everything to the royal family was betrayed after making use of her powers. They made her out as a villain, someone who betrayed them when in reality it was them who did that. When she woke up in the body of another girl who was in the process of being made out as the villain just like her, she decided enough is enough.
"I am going to marry the Duke!"
"But, milady! He is just a trash! A thorn in the side of the royal family."
Oh, he is not. She would make sure of it. Besides, he was the one who asked for her hand in marriage. Now that she has a chance at having romance, she is not going to let it go!