Who is Miss Dominatrix from Marley and Me and what is their importance?

Miss Dominatrix is the name John gives to the instructor of obedience school. She is demanding and not at all understanding. Instead of taking the time to work one on one with John and Marley or offer support to the Grogan's for their hyperactive dog, she kicks Marley out of class after the second week. She appears to resent Marley's boisterous temperament.