Mistress Abbie needed to train her slave to lick feet and that is why she chose to make sure that her slave learned to do all the things that he needed to. She made him start with her dirty soles and he had to do it as she made it clear that if he refused to do it, he would only have himself to blame for whatever would happen to him.
Mistress Abbie wanted to make sure that her ex licked her soles. She did not want to let her ex think that he could get away with whatever he had been doing. He had thought that he could do whatever he wanted but she had to prove him wrong and she did by turning him into a sole licker. He had to also endure being trampled before she let him go.