@Destynova I'd be willing to bet on there being more revelations to come, but I wonder... Perhaps the Duke's curse was Daleth's Sister's first attempt at getting rid of Sharon; maybe she wanted to do things in an indirect, but incredibly cruel, fashion, but Daleth somehow stopped it, so Sister went for a more direct approach, not realizing Daleth had predicted it and made it so that whatever Sister did to Sharon instead just put her in a coma, Sleeping Beauty style.
@destynova ... what if it indeed was the Duke that touched Sharon, which caused her to "pass" away? But Daleth put some kind of protective spell or something to instead reverse the death or prevent death and instead put her into a deep coma instead. And what if Rob saw that the Duke was the one who touched Sharon, and caused her "death," and thus Rob states that it was just an accident because he knows that the Duke, or anyone near them for that matter, may not be able to deal with the fact that they were the cause of Sharon's "death."
I didn't catch up with the manga but imagine if Daleth had no sister and was just mental with a dissociative disorder illness? But then again, it wouldn't explain the two nun in white thing from the journal and the other clues about her sister.