The round tube below the hexagonal barrel is called a tube magazine. It's not a second barrel. So not a shotgun, but a rifle. 44 (sometimes called 44-40 is a decent bet. I would not mess with her and only address her, "Yes Ma'am."
I don't what to mess with her either but she is interesting to photograph. We are working with her on a book cover. I may do some more of her to get a little more sultry.