Who is Beatriz Dargan Mackley (Beeder) from A Feast of Snakes and what is their importance?

Beatriz Dargan Mackey, better known as Beeder, is Joe Lon's insane sister. After finding her mother dead (suicide), Breeder lost a grip on reality. She is described as dirty, isolated.... by choice. It is Breeder who tells Lottie May to kill what haunts her or find a place to hide. She then gives Lottie May the knife that will be used for Buddy's castration.