The only catagory that I can think of that fits the known evidence, KC's behaviors, lies, and obvious psychosis, is that of "homocidal desperation". A desperation to turn back the clock by omission. Without Caylee she would again be the center of attention, not only within her immediate family, but also increased many-fold by the sympathy she'd receive from everyone for her "loss". Desperate to be able to live her life as envisioned by her recent tattoo (I doubt if she even felt the pain, - on any level), free of any implied guilt from not providing selfless love, committment, and responsibility, to a defenseless and dependent child. Increasingly desperate to remain "in control" without having her word questioned (by parents) or revealed (by Caylee). Desperate to meet men without the precondition of "single-mother" as a dominant theme and identification. Hedonism on a psychopathic scale.
I'm sure the "desperations" were more vast, more ego-centric, and more illogical, than discernable to the average moral and loving person, but we are talking about someone possessing neither of these attributes by any identifiable level that we all know and take for granted, - in both cases, a given.
Motive is determined solely by her perspective. And, with a sociopathic, lying, narcissistic, murderer who thrives in the "game", even a confession might be nothing more than another fictitious embellishment spewed for her own reasons of unreason.
The fault to be assigned the parents is that, after a lifetime of stirring the pot, this was the best they could come up with. They hold my utmost sympathy for their loss, - and pain, thereof. But, for totally mismanaging their roles as parents for KC and grand-parents for Caylee, I hold them ethically, morally, and responsibly, accountable.
The only consolation is that Caylee is more than fine, right now, and any tracks from tears are just from laughing too hard.