I'm sure most people who watched epiosde 1 have the same big question on their mind:
Is this Naksu or Bu-Yeon?
1. First, from what was shown, even mama Jin is not sure 100% - she unconvincingly tried to assure Cho-Yeon that Naksu's soul died and she has the right to use her body for Bu-Yeon. Whatever they did to bring her back, they couldn't use Bu-Yeon's original body, but somehow magically conjured Naksu's body. But she was still shown with petrification signs in the past in the preview. Ok, but if that's By-Yeon, mama Jin, why the cold shoulder and keeping her locked in a dungeon like room for three years? I'm not buying it.
2. Second, yes this new girl sees energy, but that was the same when Naksu was in the body of Bu-Yeon and shared it with Bu-Yeon's soul.
3. And most importantly, she's not blind. We all saw in part 1 that every time Bu-Yeon's soul surfaced into the forefront to take control, Mu-Deok turned blind. So if this new girl was solely Bu-Yeon, she would have been blind as well.
All in all, mama Jin f*cked up again. And she knows it. She mistreats the girl because she knows Naksu is still inside her. But she wants to marry her off as Bu-Yeon, because Bu-Yeon is still inside there somewhere as well and the girl can produce an heir with priestly powers.
And lastly, we also know from Cho-Yeon's words in part 1 that Jin priestesses can erease and scramble memories, which is exactly what they did with Naksu here.
Hopefully this amnesia bs plot will get resolved soon. And they won't be able to hide Naksu once she's out in the wild - many people know her face and questions will be raised how the ef that is supposed to be Bu-Yeon.