The only way that's possible is that she must have slept through the Liturgy of the Word at every Mass, as well as the homilies. During a three year period, the Church's readings cover almost the entire Bible, Old and New Testaments. If you pay attention, you'll learn the readings, and if the priest is doing his job, his homilies will 'illuminate the Scripture', and folks will learn what the Bible is teaching us.
Then the logic would conclude that the priest was NOT doing his job. Being a nun for many years I’m sure she had the base of Catholicism covered but felt that that was not enough to fulfill her spiritual needs. I’ve experienced that myself in the past. Come out of a Sunday service that was actually boring and then during the week attended a Bible study where when I left felt uplifted and said, why can’t church be like that. Sometimes it’s to do with the personality of the teacher and charisma of the leader.