I agree with what you've said here, Brini. She was the same ole Casey that we see today. She was just in different " character " at the time she was with Jesse. She is a chameleon, and just "acts" one way or another as the situation calls to fit in. It's about deception and manipulation.She wasn't faithful to JG. JG's dad caught her loving up another guy on MySpace, and talking about getting together with him, "When you come home." (I think I remember he was military).
Nothing "snapped." She morphed into a religious homebody for JG. My guess is that JG's quiet lifestyle didn't suit her. CA also didn't like the Gs. Another poster opined that CA didn't want to share Caylee. Also, KC was angry that JG wouldn't put his name on the birth cert.
KC was promiscuous before and after JG. Ryan, who knew her since she was five or six, would not give JB a character reference for KC.
She could've aborted, but I doubt that she thought about how much time and energy children need, or how totally they impact one's lifestyle. When she found out, she killed Caylee. CA suddenly demanded that KC get a job, move out, and become a responsible mother. We know what KC's response was.
KC got engaged to JG. Lately, she wanted to be married to TL, when she had only known him a month. LE found a piece of paper where she was practicing her married name with Tony-- and she didn't even know how to spell his last name. That's how serious KC is. It's about "Mr. Right Now."
She had one job in her whole life. The management liked her, and were considering her for management training. However, they also had a problem with her coming in late, sometimes, after partying. When she got bored with the job, she just stopped coming in.
No secrets, no trauma. She's just a common, shallow-as-a-teaspoon sociopath.
Good analogy, Brini... " just a common, shallow-as-a-teaspoon sociopath".
I think there may also be a touch or two of psychopath 'in there' as well.