I think she is stuck in an impossible situation. Her role in being on TV is to convince people to look for Caylee. To do that she needs to convince people that Casey's stories make sense and Caylee is alive regardless of any doubts she has. They (gma, gpa, lee) have been told so many conflicting things from Casey (often refuted by others) about what happened, where she was, etc. that it is impossible for her not to sound like she's contradicting herself.
Of course she's going to blame the media, try to get sound bites, focus on Caylee. She has clearly told the media everything useful she's heard from Casey - I don't think there's a lot to add. Her admitting to Casey's faults doesn't help anything - I'm sure her husband knows that the more sympatheitic casey seems, the more likely people will think Caylee is alive and look for her.