Maria Teresa is one of the more reliable narrators in the book because she is the only one who has a written record of the events that happened and her thoughts when they occurred. Granted, her recollections are taken from a diary, which is unquestionably created from a subjective perspective, but still, the fact that she does speak from a written record of any sort gives her narration a little more credibiity than if she were just reporting from memory.
Maria Teresa starts to keep a diary from the time she is a child, during her early days at Immaculada Conception. Minerva gives Maria Teresa her first diary as a First Communion gift when the younger girl is only ten. Maria Teresa affectionately calls the diary, which is "so pretty with a mother of pearl cover and a little latch like a prayerbook", her "Little Book". Minerva has told her that keeping a diary is "a way to reflect and reflection deepens one's soul". Maria Teresa eventually has to give up this first diary because one of Minerva's friends, Hilda, is arrested for subversive activities, and the belongings of anyone associated with her will be examined by the authorities. Since Maria Teresa had written about Hilda in her diary, Minerva takes it from her and places it in hiding (Chapter 3).
Maria Teresa continues the habit of recording daily thoughts and events throughout her life. When she is imprisoned at the age of twenty-five along with Minerva and others, she manages to secure a notebook which becomes a surrogate diary. She resumes writing about the things that happen to her each day in prison, and includes her own reflections on these events. In one of her entries she says, "It feels good to write things down. Like there will be a record" (Chapter 11).