Who is Nun that saves Pilar from By the River Piedra I Sat Down and Wept and what is their importance?

This is the nun that saves Pilar when she finds her lying on the ground outside, after leaving her friend behind. The nun gives Pilar the courage to write down all her feelings and to toss them in the river to get rid of her pain. She also tells her that love is like a soul; it never dies.