Who is Reverend Mother Sheeana from Chapterhouse: Dune and what is their importance?

Reverend Mother Sheeana is recalled as the Fremen girl orphaned by a sandworm on Rakis/Dune, raised by the Rakian priesthood and revered by the people as a new prophetess (if not goddess), and finally taken in and trained by the Bene Gesserit, Sheeana begins this novel as a Reverend Mother, the youngest in history. She is a tall, slender, austere woman with wild all-blue eyes and commands Desert Watch Station on the edge of the new desert of Chapterhouse. She is awaiting the appearance of the first worms grown on this planet. The Reverend Mother Superior Darwi Odrade, Sheeana's first teacher, suspects something dangerous still lurks in this wild girl who sculpts when fearful. Nevertheless, Odrade slates Sheeana to replace old Tamalane on the Council.