Casey Anthony may have a personality disorder. I'm not qualified to speak to that. Her actions seem to put her in the Narcissistic, or borderline, or maybe even sociopath pigeonholes. These terms are being bandied about on message boards by people who may or may not know what they are talking about.
To me, she seems like The Mean Girl.
I met many examples of The Mean Girl when I was growing up. The one that always seemed to get her own way. She would lie, connive, bully and beat until she got what she wanted. She was capable of humiliating a victim one minute and "nice-ing" her out of her lunch money the next.
The one who would walk by with her little coterie of friends and whip the skirt of my school uniform up to expose the fact that I was not wearing the regulation navy blue bloomers.
The one who would "accidentally" knock the water jar over my tempera painting right before it had to be handed in.
The one who would be so sympathetic to my loneliness in high school, and then go and tell the boy I told her I liked that I wanted to go out with him.
The one who would borrow my beautiful dress that I had designed and fitted for myself, and then tell people that she made it, but she thought she might give it to me, as I liked it so much--and then return it ruined with hair dye.
If she wanted your boyfriend, she'd get him. If she wanted your necklace, she'd take it.
She could clean out your entire record collection in an hour--or anything else not nailed down.
She is a destructive force. She is a user. When she no longer has a use for something, she tosses it like an empty beer can.
ETA: The insanity escalates. There is now a live webcam outside the Anthony residence.