Murders on the Belfry S01 E12 Episode 12

The nuns have now learned that Abbess Maria is dead. They mourn her loss full of questions. Sister Arsinoe decides to tell the other nuns everything about the secret investigations of the abbess that led to her death. Sofianos and Tsakalakis try to "unmask" Dimitris, who is behind the murder, while Karaiskos seems to have escaped them. As the nuns and Father Fanourios mourn the loss of the abbess, one of the nuns, affected by the tragic outcome, visits the police station and confesses to the murder of Petros Angelos. Who is she?