A fair amount of speculation as to the underlying behavioral disfuntion drving AB. I no doubt believe that her defense team is fashioning some sad saga of AB's existence, packed with numerous tales of abandonement and maltreatment, etc. And they are probably monitoring the various blogs and comment sections for various reasons. Nevertheless, I have come across what I think is a strikingly appropriate potential "theory" of her state of mind. I DO NOT THINK THIS IS AN EXCUSE, just and explanation.
Take a look at the Wikipedia entry for "
Malignant Narcissism". Pay particular attention to the Narcissistic Supply and Alter Ego sections. And hold on when you get to Narcisstic Rage. (I realize Wikipedia is not an authoritative resource, but it is a good starting place). This all jibes with many facets of this case, and explains the out of nowhere aspect. A person afflicted with these traits is essentially learning and training themselves to the point that her "expectations" of how she should be treated or viewed would cause her to "lose it" someday.
This would fit the frequent mention of something "happening" between E and AB that would set AB off. It may not even have been that particular day, and may not have appeared significant in the minds of anyone who observed it.
Most disturbing, is that if this complex was working on AB, the staging of this "event" was very intricate and important for a reason. Recording a diary entry. Despite the apparent opportunity, not fleeing. Leading authorities to the body. And at least one "friend" may have perhaps tipped everyone off to this by calling AB their hero. Either way the adult certification goes, AB has achieved infamy. Almost a legacy.
It's difficult to get your head around this crime being perpetrated by adolescent girl, without the backstory that is slowly emerging. IF this is the disorder she was battling, it may very well be that she was planning to do more.