If it was an accident there wpould be no need to protect herself. An accident is just that an accident. Could it have happened because Casey was not paying full time and attention, of course, but she would earn much more sympathy if she lost that baby in a horrible accident plus she could have kept her freedom. Since she is such a habitual liar, I am sure she would not have a problem making up some story about how the accident occured. I think for some reason, she had to get rid of that poor baby's body to hide evidence, be it a drugging, heat, or purposeful drowning.