I looked up a recording of “The Last Rose of Summer”, and the rose in the lyrics/story of the song seem to fit Rosanna (who obviously has “rose” in her name)...the story is about the last rose of summer that has survived all the other roses that have died and faded. Ultimately though, the narrator decides to kill it because it seems so sad that the rose is the last one, saying in the last stanza that they would choose a quick death than to be like the friendless, lonely rose. Could this be parallel to Rosanna being the rose and somehow the narrator being Betteredge/Lady Verinder breaking her off into being with people she doesn’t fit in with as some twisted Christian act in the name of helping the poor?