This mistress felt that this slave was too lazy for her and she had to find a way to deal with him. She had to make him stop his laziness and that is why she chose to whip him. And she specifically whipped his bare back and made sure he cried out in pain and that his back was painful for the next couple of days until he learned his lesson.
Mistress Redhead likes to dominate using her whip. She does not care about using anything else other than her whip to punish. This is because it is convenient, it is painful and it gets the job done. Besides that, she does not get tired when using it on losers and slaves who need to be given a piece of her mind. It always works and that is why she used it on this slave today to remind him that she was the boss.