ianthe was like “what if i didn’t have to lose anything to become one of the most powerful bitches in the universe?”, so she killed babs and lost the fight to cyntherea, lost her arm, her sister, her crown (as in memorial day), her crush and only companion on the mithraeum, the body of her cavalier, her chance to get harrow back and lock up alecto again, and probably will lose her bestie (kiriona) and her life on the next book