I'm thinking it might be a reincarnator related. Like the actual saintess swapped bodies with her otherworld counterpart to escape that fate(powers sealed), or this is the original personality who was taken over by a reincarnator but with the sealing she is now able to have control of her body again(explains the memories)
I hope it’s Nature vs Nurture Psychology.
It’s the whole
“Would a person who committed crimes still be the person they were without the memories that put them in that position?”
Sometimes people are inherently bad lol
But
It could also be that something fucked up happened that forced her into such a position.
Someone without those memories, she really has no reason to be mean.
Think of a food you hATE. You see that same food in front of you and go “eugh gross” because you remember what the food did. You remember you hate it so you act according to that hate.
But if you don’t remember even tasting it, well, then it’s just another food. You don’t hate it. Not yet at least.
-reasons she could have been a bitch
She was raised that way
Revenge
She learned that the only way to survive was by being the top leading power in the world
She could have prophesied a disaster and being evil was a biproduct of her reacting to it.
—-
People can change when their motivation vanishes.

Trying to figure out why her personality did a 180 after losing memories. I cant think of anything else besides a whole new person