Who is Margaret Shockley from Sarum: The Novel of England and what is their importance?

Margaret Shockley is the daughter of Edward in seventeenth century England. She never marries but raises her younger brother Samuel. She makes a deal with Forest to educate the boy to save him from the Puritanism of his Uncle Obadiah, who then accuses her of being a witch. She is tried and young Samuel testifies for her, saving her from burning.