Lady Tassia loves to dominate people who mess with her and the latest to do so was this loser and she had to dominate him in a way that he had never done before. That is why the mistress chose to make this loser lick and smell her feet knowing that they were smelly. He was cornered with the request and he had to do it all as there was no alternative.
Lady Tassia was fed up with this guy as he did not understand her the way she had hoped he would. She had to make sure he learned his lesson and she decided to change the mode of sending the message to him. That is why the mistress had the guy lick and smell her socks which were sweaty and stinky as she had just worn them as she worked out.