IMO, there is no evidence as yet that proves KC deliberately murdered her child. There is much evidence that very strongly suggests that she knew all along that Caylee was dead, actually hid her body and then covered up and lied to everyone, acting as if everything was fine and dandy. But nothing that I have seen yet proves how and why Caylee died, or whether it was a deliberate killing, the result of a sudden loss of control or the result of some form of negligence by KC - e.g. not watching Caylee properly around the home/yard, leaving her sleeping in an inadequately ventilated car or giving her too much medication to get her to sleep.
Her behaviour after the event appears to be that of someone who just doesn't give a damn, but it could just as easily be that of a cowardly, weak and immature girl, who believed that her lies would once again get her out of trouble. The reason that she isn't talking is because she knows it is her fault that Caylee is dead, but whether that 'fault' is actually a deliberate act or some degree of negligence remains to be seen. I think it's all the same to her - Caylee died through either her act or omission, and whichever it was, she would rather lie than tell the truth.
So, what evidence proves she intentionally murdered Caylee? IMO, if there is some, we haven't seen it yet. Even the duct tape proves nothing, unless it can be shown that it was applied whilst Caylee was alive, and that it contributed to her death.