I'd say the obvious problem is that both sides contain individuals who dislike the idea of making peace at this point, and the demons thinking like that are really not going to like a girl like this idol. Basically selling out to the humans and all. There seem to be several demons lurking around in the background of this story lately disguised pretty well as humans, I could see them assassinating a high profile target like her while in disguise to disrupt the peace. Even if they don't, the humans that hate demons might beat them to it anyway.