I am a million miles away from being a lepidopterologist, and I found the website Butterflies and Moths of North America to be very user-friendly and informative in my quest to identify this butterfly. Once I narrowed down the search to butterflies in the general popular category of "Red Admiral," I could then determine which of these butterflies my friend really was.
Update: Upon further research I think that this variety of Red Admiral is actually Vanessa atalanta. The telling piece of evidence for my opinion is the presence of the four small triangular markings at the base of the butterfly's hindwings.