Mistress Hibbins is Governor Bellingham's sister and a witch. She's constantly trying to get people to hand out with her, all "Hey, come to the witch party in the forest!" and "We shall have the there anon" (8).
Anne Hibbins was a real person in the Massachusetts Bay Colony and was executed as a witch in 1656. So, was she actually a witch? Well, the narrator keeps calling her a "witch-lady," so it's tempting to think that Nathaniel Hawthorne though so—but, we think it's highly unlikely that Hawthorne actually believed in witches. Instead, the main problem seems to be that he has a nasty temper. She's called "bitter-tempered" (2.1), "sour and discontented" (12.5), and "ugly tempered" (16.17).
But we have to say, if the whole town was constantly threatening to hang us for witchcraft, we might be pretty bad-tempered, too. Are you into grotesquely unfair trials and executions? Learn more about the historical Anne Hibbins here.