whence "Herself" as "the Mistress" or "my wife"?

[Mark Mandel]

A friend of mine just reported <http://wcg.livejournal.com/888866.html> on
his blog:

Herself writes:
>
>> I just sent the finished file of the revised* Ivan, His Booke* (almost
>> certainly to be finally titled *Captain Vorpatril's Alliance*) off to
>> Baen.
>>
>
To other fans of Lois McMaster Bujold, the quoted text as well as the icon
that wcg used on the post make it clear that the author is the referent of
"Herself". But a commenter asked

umm Im use*[d]* to the irish use of this phrase is your wife Ms B? is it a
> pen name? am I lost?
>

The blogger clarified in the particular case, and I added

Many of us in her fandom refer to her so, at least occasionally. I think
> the use for one's wife originated as a joking adoption of the use by the
> servants to refer to the Lady of the House, but I have no evidence for that
> speculation.
>

I checked OED online before finishing that sentence, and I see no mention
of that particular idiomatic use, which I have the impression that I
learned of from reading English novels and watching such Masterpiece
Theatre productions as "Upstairs, Downstairs". Can anyone help?

Mark Mandel

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