Lady Cathy did not want to deal with her assistant because she had noticed that he was lazy. She did not want to encourage laziness and that is why she chose to use her humiliation fetish to deal with him. He was humiliated and made to beg her to stop as he felt that she was going overboard. But she told him that it all on him and not on her.
Lady Cathy wanted to humiliate this guy because he did not seem to know his place. It was important for her that he knew his place and that is why she opted to cruelly humiliate him. She crushed him and she also forced him to endure the pain and humiliation that she inflicted on him. He never messed with her again or forgot his place as he knew what would happen.