Complex sentence: De Beauvoir herself was deeply religious as a child, at one point intending to become a nun, until she experienced a crisis of faith at age 14, after which she remained an atheist for the rest of her life.
Split into simpler sentences: De Beauvoir herself was deeply religious as a child, at one point intending to become a nun. She experienced a crisis of faith at age 14, after which she remained an atheist for the rest of her life.