Whateley,
Welcome to the Forum. I would have though that she could have worked for any company that supplied the Army with anything that involved sewing, e.g. uniforms, tents, webbing, kitbags, etc. Trade directories of the area might give a clue, but as a lot of these sorts of workers may have worked from home, it would only be guesswork. It's also possible that any company turning out such stuff may be turning out a variety of civilian products too. No personnel records, if they ever kept any, would have survived. I'd look under uniform makers or military suppliers, but that's a best guess.
Maurice