I've been thinking about the duct tape too. A frequent way a parent kills a child (premeditated) is to smother them. So what if the duct tape were wrapped around the head twice, so as to make sure the mouth and the nose were covered? It would mean she didn't have to stop and tear or cut the tape so much.
So chloroform could have been applied to put Caylee out, then duct tape to cover her mouth and nose. She would have died within minutes, no blood or muss to explain.
I keep thinking of the description LE gave of the tape. They said it was keeping the mouth taped shut. To me, it sounds like the tape was wound around the entire circumference of the head, but covering only the mouth area. A small child wouldn't be able to remove tape that had been applied in such a manner.
The tape (if mouth covered only) makes sense to me if Caylee was still alive and Casey was afraid she'd scream. Taking this a step further, Casey could easily have prevented this by using her own hand to cover Caylee's mouth. That's why I believe she probably chloroformed Caylee first, applied the duct tape, then left Caylee alone, perhaps to drown in the water.