It was her belief that use of a nuclear bomb was so 'off the wall', it gave the leadership a chance to save face and surrender without further loss of life.
It was also her belief that a 'demonstration use' of a nuke would have had the opposite effect.
And thanks for the info about the military only surrender, I did not know that.
The bomb as a practical demonstration of power struck right at the heart of Oriental (and especially Japanese) concepts of warfare; once you have made an unanswerable show of force and superiority, your enemy should, logically, quit.
This is the logic behind the attack at Peark Harbor, Midway, sweeping the Royal Navy from the Indian Ocean, the lighting intial moves of the Pacific War in which the Allies lost almost all of their colonies and outposts: you see how superior we are? You should quit now.
Against any other culture, the logic of the Japanese rationale would be readily understood and accepted. Not so Western culture.
A negotiated end to conflict was ALWAYS the Japanese war aim, however, they never thought they would be on the short end.