Credence and Doratea were the two younger Senjack sisters. One of the two older sisters became Soulcatcher. Credence is the one who was actually killed and imperfectly resurrected, Doratea is the one who went looking for her, found her, was taken to the Ghost Country, came back, became The Lady, and did her best to confuse the issue of who was who.
I was discussing this with a friend last week, and he pointed out a much scarier possibility, which handles another loose end. What about all the clones of Doratea that started turning up during PoS? They get taken away to the Tower, and after that, we learn very little more about them. They all have vast magical potential, and one reason for the memory interference must be to hide their existence. A logical possibility is that there wasn't just one Lady after that, but dozens. The Doratea who was Named and de-powered at the Barrowland was one of them; the Lady who went south with Croaker was a different one, and "regained her powers" by revealing them at her own pace. This also makes sense of why the Empire didn't fall apart after the Naming of the Lady; there were plenty more of her. -- John Dallman, jgd@cix.co.uk