Suur Trestanas is the Warden Regulant of the Concent of Saunt Edhar, in charge of enforcing the Discipline of Saunt Cartas. She is said to be in a liaison with Fraa Corlandin of the New Circle. She is fairly intelligent, but strict and unyielding in her position.
As Warden Regulant, Trestanas is answerable to the Inquisition for the avout adherence to the Discipline and seems somewhat anxious to make a good impression on the two Heirarchs visiting the concent during Apert. She is either suspicious or jealous of the amount of friendly attention Fraa Erasmas attracts and, on Tenth Night at the end of Apert, Trestanas assigns five chapters of the Book to him as penance for brawling with Saeculars. This not only removes Erasmas from further contact with the Inquistors, but denies him the chance to say goodbye to Cord before she must leave him in the Concent for another ten years. The penance in no way fits the crime, but avout can only appeal a penance of six chapters or more of the Book.
Erasmas's suspicions that the heavy punishment was a ruse to deny the Inquisition further access to him are borne out when several weeks later, his examination on the bizarre material in the Book is almost cursory and over by dinner.