The book said she needed her, alive. She would just as happy to kill her and siphon her magic, but that wasn't what the Book wanted. It needed the Empress alive. There was something that needed to be unlocked in her, something that would bring Him out. The Empress would be sacrificed.
"Keep an eye on them." She said, speaking to the so called King of Westeros, Stannis Baratheon.. There were at least Seven Kings of Westeros, but he insisted on calling himself THE King. He was no king, no mortal man was. There was only one King, One God, and his name was Malkieth.
"She's taken a liking to the boy, we may be able to use this to our advantage. He doesn't know his magic....we need to keep it that way." She told Stannis as she turned to him walking up to him with the large tome in her hand.
"How has your son fared with the other Hallows?" She asked, she would need all four hallows to gift to the UnSeelie King once he was freed. Without them, he would destroy them all, she wanted to be at his side, she needed to be his bride, that was her destiny. She already had his book, now she needed his Sword, Cup and Song. The Song proved the most elusive, no one knew what came of the song, some say it was given to a mortal upon it's birth, which is why she began these fighting pits, trying to weed out the mortals born with magic yet none of them showed any gifts that would be proof fo the Song.
The Song of Making could create and destroy, someone with that gift would be the most powerful. She'd thought it was the Dothraki, but no, he was just large, and just strong, he could heal but he couldn't create....they still hadn't found the Song, The Sword and Cup should be easier, it was tangible.