Lady Stefanie wanted to humiliate this boot licker and she did it with her boots. The mistress had to make sure that she dominated as well as humiliated this loser and this was done using her boots. She did not want to let the guy go without a little domination so she trampled him before she let him go. By then, he had learned to fear the mistress just like she wanted.
Lady Stefanie wanted to teach this guy that he could not afford to piss her off the way he had and so she turned him into a boot slave. She made him lick her boots and when he was done, she used the same boots he had licked to trample him. He was in pain and he was humiliated as well so it was double torture to the poor guy.