The ol' "blame the parents" routine! The "chicken or the egg" thing. I don't know nearly as much about all this as some of you do but personally I do see it as more that her parents trying to cope with Casey's behavior rather than them being the cause of her behavior. They have probably been trying to cope with her behavior since childhood! The parents themselves had already been victimized by her more than once from the chaos she created in their home. From what they said, she had stolen many, many checks from her mother and probably also kept their finances in chaos.
I'm sure they made mistakes as parents - we all have. And I'm sure there are things they would do differently if they had do-overs. But they also raised another child, Lee, who may have his understandable quirks but overall seems to be a normal functioning adult. If they were such horrible, awful parents this doesn't seem logical at all!