Who is Reverend Mother Darwi Odrade from Heretics of Dune and what is their importance?

Reverend Mother Darwi Odrade is the Bene Gesserit Senior Security Mother who bears a striking physical resemblance to the Imprinter Lucilla, sent to Gammu to prepare the ghola Duncan Idaho for his mission to Rakis, Odrade is a descendent of the legendary Siona Atreides. Born to a Bene Gesserit Sister and raised until age six by foster parents on Gammu, Odrade is then claimed by the Sisterhood and undergoes standard training, survives the spice agony, and is sent to Al Dhanab for intense physical conditioning to prepare for service on the desert planet Rakis (Arrakis/Dune).