Harrieta Bilk
First appearing in A Hat Full of Sky (and returning in The Shepherd's Crown, in which she's described as a "lass with a squint"), Harrieta is a young witch in the Near Lancre coven led by Annagramma. In the true role of bullying dressed up as leadership, Annagramma made fun of Harrieta for 'being unable to do anything about her squint'. Granny Weatherwax would always say that a witch needs to have a good squint, so this is another sign of the gap between Annagramma's idea of witchcraft and the reality.
In The Shepherd's Crown, after Granny Weatherwax's death, Harrieta is the witch who completes the treatment of Jack Abbott, a young lumberjack whose injured leg Granny had been seeing to.