The Clique/WMG

The books are actually a stealth warning to not act like the Pretty Committee.
One of the things on the Fridge page under Fridge Horror is that these girls are going to be seriously fucked up when they're adults. If any tween girls who read these books figure that out (and I'm sure some of them must have. Tweens are smarter than you think), well, why would they want to act like them? I pray to God that this is true, because if it's not, I really fucking hate these things.

This is a Stealth Parody.
It has to be. It HAS to.

This is a Self-Insert Fic made by Massie
In reality, she's even more pathetic than Claire. The rest of the Pretty Committee she either made up, don't acknowledge her existence, or are on the same level as her.
 * Good God, I hope this is true.

Adding on the WMG above, the real Claire is even worse than Massie
She's a Complete Monster, and the other girls wrote this as a Revenge Fic of sorts that got way of hand.

Still adding on the Self-Insert Fic theory, this is Wish Fufillment for everybody
The real Dylan is genuinely overweight, and real Alicia is flat-chested and Hollywood Homely. Not sure about real Kristen, though.

Massie is a sociopath.
Does horrible things with no motivation? Check. Cold nature? Check. Controlling nature? Check. Lack of guilt? Big check.
 * Plausible, but Massie has been shown crushing on boys. Most sociopaths feel no attraction to anybody.
 * According to my source, some sociopaths are overly promiscuous. But you have a good point. More sociopathic traits Massie has: views people as objects and not people, early behavior problems in childhood, lack of a realistic life plan, overly self-centered.
 * Does she have any issues with personal boundaries, though? I only know about male sociopaths, though.

A sequel book will come out taking place after high school
It will be dark and disturbing, but oh so satisfying.

Massie will become a future series' Big Bad
If you thought she was bad as a middle-schooler...