Why was Virginia called an angel in "The Canterville Ghost?"
Angels are messengers who travel forth between heaven and earth, interceding between God and humans. Virginia is called an angel because she intercedes on the ghost's behalf. She weeps the tears he is unable to cry, and she says the prayers he is unable to speak. By interceding for him, she paves the way for him to be forgiven for his crimes. She shows the remorse he feels but can't express. By interceding for him, she paves the way for him to go to his final rest, which is what he longs for more than anything.
Angels are associated with purity, and Virginia is like an angel in that sense too. She is pure, a 15-year-old virgin, and she has a kind, compassionate heart. Unlike her brothers, she doesn't ridicule the ghost but is able to empathize with his pain.