I haven't read this entire thread but most of it, so excuse this post if this has already been said.
But I find i VERY ironic that in one interview with LE, KC's friend (I believe it was Amy) stated that KC would not have to be asked about the whereabouts of Caylee. She would offer details often of where she was at with the nanny. And even offered up that she was sad that she was not seeing much of Caylee but she was better off having fun going to disney and the beach and not dealing with all the drama (made up drama, of course) of the family.
Then later on in the jail letters to Cookie she states:
Ive had to forgive what happened to my Caylee, but Im still angry. Shes safe. Shes in Gods loving arms. In a lot of ways, Im content by the fact that she will never have to have her heart broken or see the constant negativity that our society breeds, nor will she ever be abused or taken advantage of. The clock is ticking and the end of days is near. I can feel it.
http://www.foxnews.com/us/2010/06/25/casey-anthonys-prison-letters-released/
I believe she felt that Caylee was better off dead from the time she killed her and probably before. This made it OK in her mind to go off and live. She was lying to Amy about Caylee being off to the parks and the beach but there was some inkling of truth to it even then. She knew she was dead and she believed she was better off.