@MCX01 Well I commented the same on the previous chapter, but im assuming and id like to stress that this is my guess, she was a reincarnator and got into Raelianas body.
She knew about the poisoning so did the soul swap to become the protagonist. Our mc then got into Raelianas body.
Because assumadly Beatrice knows about unstable souls she is trying to kill of Raeliana to fix it.