i'm not sure what's she's doing but i can infer. i think she may have also come back to life like pereshati that's why she knows a lot about everything and the blood specifically. Since phineas said that there might be a connection between their curse and people coming back to life, i can assume that she knows something about that too and might have something planned to "get him"
So I read a spoiler it said that the person in the princess’s body is not the real princess but a cursed witch who was in love with Theo in a past life. They said that she was cursed because she broke an oath and became immortal since then she dies and born in different body everytime and she met with him while she is in the princess's body

Someone give me a spoiler on the princess is she doing some sort of voodoo like will she do something pls spoil me