In Chapter Five of "The Canterville Ghost," Virginia helps the ghost by enabling him to enter the Garden of Death. She does this by accompanying the ghost through the wall of the Tapestry Chamber and helping him to receive divine forgiveness for his earthly sins. Remember that the ghost cannot do this for himself as he has no tears. By doing this, Virginia has fulfilled the prophecy which is written on the library window. This was a necessary step in bringing about the ghost's death and restoring peace to Canterville Chase. 

Virginia never reveals the exact details of her time with the ghost. She does, however, tell her family that the ghost really was sorry and that "God has forgiven him." The ghost is so grateful to Virginia that he gives her a box of jewels, a permanent reminder of her role in bringing about his salvation.