Who is Lucy Pensevie from The Last Battle and what is their importance?

Lucy Pensevie returns to Narnia with her brothers, where she witnesses the destruction of Narnia. While there, she meets her old friend Mr. Tumnus, and Aslan tells her about the accident that occurred in which she died. Lucy was afraid of begin sent home, but Aslan explains to her that they will be there,and that the real Narnia is the after life.