I'm gonna be honest here (regardless of how I may be judged) as I always am when I speak of my "former" self.
In Casey's call home from jail I heard me in her tone as SOON as her mother picked up that phone. This is my take on Casey..
She knew exactly how to speak to her mother, just the right words and just the right tone to get her to soften. By what, the 3rd sentence, her mom was calling her sweetie. She knows the more she lashes out while still appearing hurt, her mother will cave.
The dismissiveness and lashing out with her friend, yup! She called for a reason (Tony's phone #) and her friend was getting in the way of that, who cares what the friend has to say. But then she catches herself, realizing she may need something from the friend sometime soon (bail money, another persons #, to pick her up when she gets out of jail, etc..) and thanks the friend while calling the girl sweetie or honey and telling her she loves her.
The brother? She has no control over him, none and she knows it!
The dad is a bit harder for me to figure because I didn't grow up with a dad and I don't know how "normal" fathers and daughters interact but it appears he has simply gotten used to his wife allowing Casey's behavior and cleaning up after her all these years so he stays out of it. I don't think she has any control over him, she didn't even ask to talk to him when she called from jail. I also suspect Casey (and Cindy's enabling) may be the reason he and Cindy had split up in the past. IMO Cindy would side with and even choose Casey over her own husband
Casey is manipulative and lonely and angry and empty inside. She lies and steals and parties and has sex with whoever makes her feel good about herself in attempt to fill that hole in her being.
She will (has, I'm certain) suck people dry, use them up of everything good they have to offer and leave them, less than.
Addict? Bipolar? Borderline personality? or just some who killed her kid? I think we can all find little things about Casey (and other mothers who murder their children) that remind us of people we have known or text book examples or hell, of ourselves.. regardless, no excuse is good enough.