Background & Early Life
Not much is known about Catherine's early life. She is a nun at the Saint Francis' Boy's Home, the orphanage where young Nathan Drake lived. Following his frequent mischievous incidents at the orphanage, Sister Catherine constantly gives him lectures.
Uncharted 4: A Thief's End
Following a fight between Nathan and a boy named Edward, Sister Catherine was in Nathan's room giving him a lecture about constantly getting into trouble and regarding the fight. Before leaving, she tells him no matter how hard she tries, he seems insistent on going down the same troublesome road as his brother.
Later that night, Catherine and Father Ryan Duffy where having a discussion about Nathan. She suggested to possibly expel Nathan from the orphanage for his constant mischievous behavior, but Duffy seemed to discourage that idea, stating how it is their job to help boys like him. He told her that he will speak to Nathan in the morning, and both wished each other a good night.
Catherine begins smoking secretly in another room, and fails to notice Nathan sneaking behind the furniture. Before she can finish, Duffy returns, causing her to quickly put out her cigarette, and asks her to open the main gate for him, as he forgot his keys at home. She than leaves the room as Nathan leaves through the window, the last time he ever sees her.