Esther is the only book in T’nakh with absolutely no mention of God (by any Name). Much as the Midrash interprets some occurrences of “the king” in Esther (e.g. 6:1) as a reference to God, this is certainly not p’shat. Why is this story even included in the Biblical canon?
Even if the apparent turning point of the megilla takes place later on, from a certain perspective, Esther's agreement should also be viewed as a "turning point" that anticipates the later, more obvious one. The essence of this idea lies in the question of the identity of the "hero" of the Esther narrative.