Lady Soles wanted to dominate this guy and she did it without caring what the guy felt and what he was going through. All that mattered to the mistress was that things worked out her way and that it all happened in the manner she had planned for it to work. That is why she used her giantess butt crush to dominate as well as to degrade and it worked.
Lady Soles had a lot of time on her hands and she felt that she needed to do something with it. That is why she had to go out of her way to teach the guy a lesson that no one had ever taught him. The mistress turned the guy into a little man and tormented him for her own fun and when she had had enough of it, she let him go. He was shaking like a leaf.