Lady Scarlet felt that she was being taken for granted. She had to demand respect and since she was not getting it, she had to do something in order to get it. She chose to beat the crap out of this guy after she had stripped him naked. He was in pain as she ballbusted him and that was when he learned to fear and to respect her like she wanted.
Lady Scarlet is the kind of girl who does not like to be pissed off because she loves revenge. This guy pissed her off and he had to deal with the consequences as she punished him in a savage manner. The mistress did not care what he felt. All that mattered to her was that he was in pain and to make sure of that, she blindfolded him and tied him up while he was naked. Then she tortured his balls and his nipples.