Floella, it doesn't have to be too elaborate, check out the internet for colours etc. You could get away with a skirt and tie of the same colour, white shirt, some homemade epaulettes for the shoulders, and I am sure it couldnt be too difficult to make one of those little 'Dads Army' pixie hats, pair of tights and black shoes.
First thing I would do is troll the internet for photos from that era and see what comes up but your daughters suggestion is completely on the mark too.
Happy sewing
warpig