Who is Reverend Mother Superior / Grand Honored Matre Murbella from Chapterhouse: Dune and what is their importance?

Sexually bonded to Duncan Idaho, the former Honored Matre postulant from Gammu, kidnapped as a child and forced to learn how to mesmerize males sexually, Murbella begins this novel living with Idaho and Scytale, the last surviving Tleilaxu Master, aboard a grounded Bene Gesserit no-ship in the space field on Chapterhouse. Murbella has domesticated Idaho and can be humorous, showing no contrition about sacrilegious doggerel she is caught posting. Pretension and discipline annoy Murbella. As part of her Bene Gesserit training, she has switched successfully from melange substitute, which causes eyes to flicker orange when angry to melange, which causes blue-in-blue eyes. She remains furious that Idaho turns the tables on her and addicts her sexually, but they have three daughters and love one another - despite the disapproval of both sisterhoods. A fourth is on the way, but this does not slow her training.