etymology of and that is all she wrote

what is the etymology of “and that is all she wrote” ?

Well, according to The Word Detective, it comes from the ‘Dear John’ letters that GIs in WWII sometimes received from their wives or girlfriends announcing that the relationship was over: “Dear John: It’s over. Mary.” No reason, no apologies, no chance or getting back. That was all she wrote.

http://www.word-detective.com/100699.html#allshewrote