I'm twisting in the wind with exactly the same thoughts. And here's one more possibility--Some reports describe the clothing found with Caylee's remains as a swimsuit. Now, according to Cindy, on the evening of 6/15, she and Caylee swam in the backyard pool. (Either before or after the huge blowup between CA and Casey.) That opens up the possibility that when CA took Caylee out of the pool and into the house, she handed Caylee over to Casey, and said something like, "Get off your @ss, Casey, and act like a mother for once. Your daughter needs a bath and dry clothes, and then she needs to go to bed!"
And when Cindy left the room, Casey grabbed Caylee up, put a towel or sheet around her and stormed out, never to be seen again with Caylee.
That would account for a swim suit and towel or sheet being in the bag with Caylee's remains--if indeed those items were found in the bag.
But what about the book Caylee had been reading to GGF that morning? How did it get in the woods? What a puzzle!