Or if she IS the creature, and is being kept there to protect everyone else?
that would be VERY OUAT.
Like, maybe her mother died in childbirth (which is why we got no hints of casting for her) and it was really traumatic circumstances, and so some of her mother’s tormented spirit went into the baby, (trying to tie this back to how the Grudge curse came to be), and it can affect her in some way that makes her dangerous in a possession sorta way? And so we don’t actually have a separate Mother Gothel type character, because it’s the spirit of her actual mother that means she has to be kept locked up, so she’s not a danger to anyone. And maybe she’s not allowed sharp objects lest she be a danger to herself, and that’s why her hair never gets cut.
If it’s a situation like that, where she’s sort of possessed, I could maybe see Rumple taking an interest in her, (he could be the hooded figure), because he’s sort of possessed too? Maybe he had an idea of how he might free himself, but needed a guinea pig to test it on first? Maybe Rapunzel’s supernatural connection with her mother, and Rumple learning about that, could go some way to explaining why both Pan and Rumple had to die?