MissAdventure, the woman was not in her right mind. She had what's known as an adjustment disorder which is an abnormality of the mind that impairs her mental responsibility for her acts.
In other words she'd gone through so much psychological abuse in her marriage that her mind was in such a state that she wasn't responsible for her actions when she murdered her husband.
She now has to live with that for the rest of her life and whether she finds peace of mind remains to be seen. At least her sons are there for her.