No matter how much she looked at it, Katherine couldn't imagine Grandpa Theo being the bad guy. He was warm and loving, and…he just couldn't be that person. She refused to believe it.
She sometimes stayed at the Young Mansion whenever her parents had to travel out of the country. Katherine loved spending time with her grandfather, so she always looked forward to staying there. It was Grandpa Theo who took care of her. He fed her, helped her with homework, and took her to places where they created memories together.
Of course, she might just be biased. But that's not the kind of person who kills someone and hides the truth from the world. Granted, she knew she did bad things, but Grandpa Theo was not that kind of person. There's so much kindness in his eyes to even think that he could do something like that.
It's why she didn't accept the butler's words.