In Terry Pratchett's Discworld novel 'Wyrd Sisters', which of these are not one of the three main witches?

In Terry Pratchett's Discworld novel "Wyrd Sisters," Winny Hathersham is not one of the three main witches. The main witches in the novel are Granny Weatherwax, Nanny Ogg, and Magrat Garlick. Winny Hathersham is a character in the story, but she does not hold a significant role as one of the main witches.