As I wrote there had been an execution of a lady by hanging in Kentucky (Susan Eberhart in 1873) and the Governor at that the time did not commute her sentence, so I think the people had an aversion for this type of punishment for ladies (maybe that ties back to your comment on culture). The pressure had to have been enormous for Colquitt. There was enormous publicity and thereby interest in this trial. One of her “white knights” wrote in the “Atlanta Constitution” a story headlined: “Mrs. Southern’s Neck”, and declared “that women are instinctively unable to commit murder except under the influence of whiskey or while otherwise not in full control of their senses”.
I have not found anything of what was his mind-set in the decision process and I wonder after all he had seen fighting the war, had he developed a more sympathetic nature.