Mrs. Cardigan

Mrs. Cardigan was Arthur's former piano teacher before she sent him to Dr. Fugue. Despite being Arthur's former piano teacher, she only appeared in "Arthur Plays the Blues" where Arthur is being transferred to Dr. Fugue right after she retires.

The book based on the episode implies that Dr. Fugue was one of her past students.

Personality
Mrs. Cardigan is easy-going and gentle and would offer each student a cookie for having a wonderful lesson. Her favorite flavor of cookies is double chocolate chip. She is much like Miss Sweetwater and Mrs. Fink in terms of teaching reputation.