Is it possible/likely to have her working in a factory making naval uniforms and, on the side, taking in piecework to sew at home? Would that kind of work be available to a young woman in Tokyo at the time? (I'm assuming that she looks older than fourteen and can lie convincingly about her age if need be.)
Also--and this is a very minor detail, but would she wear the western factory girl's "uniform" of dark skirt and shirtwaist blouse? In canon, her brother has a flashback to his childhood, and he's shown wearing a shirt and short pants.
My Google-fu is failing me--I've tried various combinations of Japan, garment industry, women's fashion, clothing, shirtwaist, western dress without much luck.