I can't see charging them as adults either. Although I admit when the story first broke, my first instinct was they should be charged as adults. That's why the recent trend of American court systems using emotion to dictate the law over logic or reason is problematic to say the least. I'm noticing more and more of this recently. Emotionally you can't help but be outraged, and you feel like kids are growing up faster and faster and have less empathy than older generations. But that is a biased view, and I can recognize my own bias. That's why I know better than to let my emotion dictate justice for these girls.
While I don't know their mental state now, I'm willing to bet they are past that age where imaginary things seem almost real, and realize how stupid their petty obsession was. Reason and logic seem to indicate that these won't be career criminals and likely repeat offenders. I doubt either one will be particularly productive members of society, and they will eventually get knocked up and spit out more worthless members of society, but we can't exile people to prison for being stupid.
