Lady Rockabella had nothing to do with her slave as he was not the sharpest tool in the shed. She did not want to spend more time with him than was absolutely necessary as she was sure that it would lead to her punishing him and that was not something she wanted to happen. So the mistress turned him into a sock slave and he had to lick the dirty socks.
Mistress Cleo wanted to make her friend see some sense because she was afraid that her friend had thrown sense out of the window. She was about to make a mistake he would regret and it was mistress Cleo's duty to stop that from happening. So she used her smelly feet as well as smelly socks to dominate and humiliate her friend to make her realize what she was about to do was not good.