Who is madame joanna in Catherine Called Birdy?

In the book *Catherine Called Birdy*, Madame Joanna is a healer and a midwife. She lives in the village of Lincoln under the rule of King John of England. She gives Catherine herbs to help her get pregnant, and attends her when she gives birth. She is sometimes thought of as a wise woman and has magical skills, but she is only a midwife and healer.