Craig Howell, who uploads photos from every vintage motorcycle event in the Bay Area to his website (for example, his page on the 2006 Legend of the Motorcycle), sent me this photo, from a friend's family album.
The woman is Erma Barth (soon to become Schopfer - that's an engagement ring on her finger), and the photo was taken around 1933 near Thale, in the Harz Mountains. March 6th, 2008 would have been her 100th birthday - happy centenary Erma!
The bike is a German Triumph (TWN - Triumph Werke Nuremburg, founded in 1903 as a branch of the English Triumph motorcycle factory; click here for a timeline - TWN became autonomous after the '29 stock market crash) two-stroke, which looks to be mid-20's, and around 250cc. Its small engine capacity hasn't stopped the bike's owner (Erma?) from loading it up with accessories, which include acetylene AND electric lighting (there's a small spotlamp on the handlebars), a motorcycle club pennant, heavy saddlebags, and the biggest passenger seat I've ever seen (which just might be the only comfortable passenger seat for a rigid frame).
What dates the machine to the early/mid 20's are the 'dummy rim' brakes, which supplanted the useless stirrup brakes on Veteran machines (made until 1920), but were themselves superseded by drum brakes starting around 1923/4. The first front drums were tiny, only 4" or 5" in diameter, and were basically decorative. On my 1925 Sunbeam, you can push the machine along with the brakes hard on - I've done this on early Nortons as well.
I'd say that German machines in general were much more robust (read; heavy) than their English counterparts, but of course the Yankee machines topped them all for avoirdupois. I don't know what this says about 'national character', or the quality of the roads in different countries, or perhaps the expectation of durability/longevity of owners.
Erma is wearing an interesting outfit - wool knee breeches and jacket, high stockings with Mary Janes, and an adorable beret. Not especially figure-flattering, but functional, and totally unisex (except for the shoes - only very young boys wore 'Buster Brown' shoes; by the way, Mary Jane was his sister in the comic strip).