Why did Virginia wish to retain the empty casket of jewels in "The Canterville Ghost"?

The pure Virginia helps the Ghost die and go to his final resting place in peace. In return, he gives her a casket of valuable Canterville family jewels. Virginia, being an American brought up on sturdy Republican principles, has, her father explains, no interest in the costly "trinkets" or "vain gauds," as Mr. Otis describes the jewels. However, she would like to keep the empty casket as a remembrance of the Ghost. As Mr. Otis puts it: 

Perhaps I should mention that Virginia is very anxious that you should allow her to retain the box, as a memento of your unfortunate but misguided ancestor.

However, her father is surprised that Viriginia would even want the casket, calling it medieval and blaming her interest on it in having been born in the London suburbs rather than the United States. 

The current Lord Canterville insists, however, that Virginia keep both the casket and the jewels, which in the end, she does.