I'm going to write this fast -- I'm in the middle of final exams -- so I'm hoping some allowances can be made if I make a misstatement without having an attack launched. These are only my ideas and I never meant to present them as the last word on the subject. I raised this question merely as that -- a question -- something I thought might be an interesting idea to someone, maybe someone who writes fanfiction who might see possibilities in my suggestion of one possible interpretation of Joanna Mill's character. Since I posted only my thoughts, I did not attempt to adduce evidence to back them up as I might try to do were I presenting a "case" for, for example, a case for who Victoria Winters' parents really were. But in light of rather pointed challenges to my thoughts, I'll try to think what conveyed my impressions -- though I don't know if I can provide the kind of evidence people are asking me to produce.
The ghost of Joanna Mills seemed unique to me. I think the main thing was her corporeal presence rather than the transluscent, fleeting entities that characterizes so many ghosts on DS. Within the context of the 1840 storyline, we might compare (or contrast) Joanna Mills to the other ghost we're presented with, that of Daniel Collins; they are obviously very different in form and in the way they appear and are presented.
Joanna reminded me of Angelique in the 1795 courtroom scene. My thinking on Angelique may differ from that of others, because I didn't view Angelique as a ghost. In the past, I've written at length about the resurrection appearances/bodies on DS in contrast to the ghostly entities. In my view, Angelique resurrects on DS and never comes back as a ghost.
In my opinion, the DS writers were familiar, at least having a passing knowledge, with much classical literature including the Bible. In the New Testament, Jesus returns from the dead -- but in his own words, he is not a ghost. Rather, he is flesh and blood and invites the disciples to touch him as proof of this. Interestigly, Joanna Mills echoes something very simiilar when she tells Daphne that she is real, not a ghost -- I think she even says something to the effect to touch her, feel her hands -- they're warm. Angelique says nearly identical words when she appears to Victoria Winters when she has imprisoned the latter in the Leviathan storlyine (I think that's the the right storyline). Both of these instances are examples of allusions to the New Testament; and of course there are other belief systems that speak of the body being physically resurrected. In the New Testament, after his resurrection, Jesus appears and disappears at will in his new physical form, as I see Angelique also doing ... and possibly Joanna Mills.
Every other ghost on DS that I can think of is always recognized as being a ghost by others. It's true that the very corporeal-appearing Sarah puzzles David and Victoria for que a while, but eventually even they realize that Sarah is a ghost. Joanna Mills is different. Not only does she fool all of the mortals, her true nature eludes even Barnabas, Angelique, and Judah -- the last two of which, especially, might be expected to recognize a ghost via their own supernatural powers and knowledge. Since they don't, that suggests to methat Miss Mills has some special, unique properties setting her apart from many other ghosts.
Samantha is the only one who maintains that Joanna is a ghost, but that is not based on any ghostly properties or actions of Joanna but because Samantha knows she killed Joanna. (Incidentally, I still don't think this happened at Widow's Hill, as others have mentioned again in other threads; but I admit I may have misheard the original scene and also misheard latter commentary by other characters about it. But if so, I misheard dialogue on at least two occasions indicating that this took place on the sanitarium grounds.)
So, I wondered, idly, how it is that Joanna might have some extraordinary or special aspects as a ghost. Is she casting a spell on everyone? Could she possibly have had powers in life that have carried over beyond the grave? Yes, I know there is no evidence for this -- it's just a thought, and it would be interesting what the DS writers might have come up with had Joanna Mill's past and character been delved into much more.
This explanation obviously won't satisy many posters here as it doesn't rise to the level of proof, but all I can do is try to explain my impressions to which I hoped to add a dash of creative thought.
