This feels much more likely. The possibility that it was someone else is ever present of course, but the likelihood seems to be dwindling. Sure the gun purchase in advance and her going over there are some hints in the other direction. However, it's the post-incident behavior that is really pointing toward this being a heat of the moment without a firm plan kind of situation. The time between the camera catching the SUV and KA getting home, replacing the gun, running out of town kind of suddenly, having to deal with a new identification after the initial fleeing, the back and forth in NYC/New Jersey, the timing of the presumed movements, involving her family to some extent, the father's statement, etc. It all seems a little last minute and kind of bungled a bit if this was a plan. It wouldn't seem rational to return the gun to its place while planning to take off anyway. Involving her family after the fact when it seems like an easy trail to follow although taking time to uncover and would be incredibly dark if the family was in fact involved before the fact. I wouldn't really believe that would ever happen. It's possible KA thought she could get away with it ultimately without having to flee but if it was truly premeditated, it should have occurred to her that she would be among those looked at. It's possible she didn't have any firm "plans" other than arming herself until she realized that CS had in fact been with MW that day and her "shaking" anger took over and she went to either scare MW and pulled the trigger in a fit or it was heat of passion in the moment with some pre-planning for the possibility this would arise. In any event, if KA is in Canada, that is a convenient place to escape to but not really a place to try and avoid capture and prosecution.