Verna Got Away With Murder!
Spoilers!!
I just watched this again, and I learned that Verna shot Ma Jarrett in the back because she was about to kill Big Ed.
Verna cleverly lets Cody 'force her' to tell him how Ma died.
Cody kills Big Ed, the only person besides Verna who knows the truth.
At the end of the movie, Verna is the only member of the Jarrett Gang left alive, and she was not a full participant in any of the gang's crimes. She'll probably get a light sentence, since the police will assume that Big Ed killed Ma.
Verna never got the punishment she deserved. When you think about it, Verna was the most cunning, wicked member of the Jarrett Gang.