What is Casey's official mental status? Has she been tested?

You know, I personally know of a really truly compulsive liar, and it's absolutely appalling and disturbing the things she lies about. I don't know if compulsive lying qualifies as a legitimate mental illness, but the girl that I know definitely has some mental issues that allow her to believe that such blatant, manipulative lying is acceptable. The similarities between the type of lying and lack of empathy my acquaintance and Casey both exhibit is really striking. After my acquaintance's father died, she went out to shop and party. I actually hope these two have mental illnesses; at least, then, I'd have some hope left for the human race.