This was my immediate thought, she caught him with one of the girls. Then one minute later, this comes to mind: the oldest daughter, having experienced whatever, sees dad about to do same to one or both of her younger sisters and she is the one who took him out. 10 is not too young in Alabama to know how to use a gun. Mom throws the girls in the car and takes off, no real effort at hiding, just gets on the run, why they got cuaght so quickly.
Total speculation on my part, I realize ... it comes from one too many "American Justice" stories, I suppose. Just that we keep hearing these tales of *typical American family* time and time again.
I think you're smoking catnip. First, the girl is 8 years old and doubt she could or would shoot her own dad. Secondly, he's dead. If anything his wife is probably crazy.
Apparently no speculation is too wild.