What do you learn from the character of Sheila Jack?

A twelve-year-old girl named Sheila Jack was raised to be a shaman, and draws the admiration of the other students when she arrives. Fearing her influence, the nuns force her to recite the catechism at all hours, until she goes insane and is taken away to an asylum. I think we learn that the cruelty of the nuns and the "evil" of the school was too powerful for this young shaman.