Amma - I think it has to be more than just abuse. at some point, she failed to develop a conscience or empathy for others. that usually happens when a child fails to bond with the mother. for whatever reason, Casey failed to bond with Cindy as a baby. that thus made her unable to bond with Caylee, or empathize with any of her victims. If she is so callous as to lead JG on for months thinking he was the father, to steal from her own parents and grandparents, to steal from her friends, and to lie to everyone...why should we think it should be different with her own child?
That was just one of several contributors/risk factors I listed. The bonding issue is #1. But not the only. There are several things that come together to create the ingredients for success so to speak.