Sandpiper Quiz: What is her name?

We don't know the answer to this question. This lovely swallowtail butterfly came on Sandpiper for the second day of our trip through the Dismal Swamp canal. She accepted an offering of water and stayed to drink for half an hour then as we reached the northern end of the canal she left us. We haven't been able to identify her in any of our books. Can you help?