Lady Scarlet needed to trample this guy because she was fed up with the way in which he acted. She had to teach him a lesson and she did this with her boots. But that was not all as she felt that she had to inflict more pain on him so she did this with her trampling and stomping as she jumped on him and she stomped him painfully with the help of her friend.
Lady Scarlet was pissed that her slave was forgetful. She had given him enough chances to change but she felt that he was not changing the way she expected him to. And so she had to teach him how to behave as she did not want him to continue being forgetful. The mistress used her shoes to trample him and make it as painful as he had never experienced it before.