adj. Complete, finished, over with. Not sure about the origin. Somebody fill that in for me.

You're on the right track with a song's lyrics. But wrong song. 1950's Hank Williams (that's THE Hank Williams) wrote "Dear John" 'bout his woman leaving him and taking him to the cleaners--the Dear John letter was "all she wrote".

There's a song called "All She Wrote" by Default. Lyrics:

Something's wrong with your mind
It won't think of me anymore
Was it all a waste of time
Tell me why was I such a chore
Broken bottles empty
Cut my mouth so I can't say

Today was that day
It was that time
And that was all that she wrote for me
You fell away
I don't know why
And that was all that she wrote for me

Lying here in your bed
The one that you liked to do it in
Pieces of long brown hair
Are all over it and still in my brain
i can't explain
What it's like not knowing if I'll ever cross your mind

Today was that day
It was that time
And that was all that she wrote for me
You fell away
I don't know why
And that was all that she wrote for me

Sleep through the day
Fight through the night
Seven a.m. and the tv is white
Covered in snow
I never knew that hell could get so cold

Today was that day
It was that time
And that was all that she wrote for me
You fell away
I don't know why
And that was all that she wrote for me

Today was that day
It was that time
And that was all that she wrote for me
You fell away
I don't know why
And that was all that she wrote for me

Something's wrong with your mind
It won't think of me anymore
Was it all a waste of time

So your definition sounds correct, but I'm not sure of the origin either. All I know is I think this song backs up your definition.