For many years I thought this was a Special Policewoman
She has black horn Norwich City buttons. She has a police duty band on her left upper arm and a whistle chain and a truncheon. Her cap badge is unclear but appears to be a wreathed crown. Norwich Special Constables were awarded a silver star worn on the right sleeve after two year's service. Constables normally wore the striped "duty band" on their cuff.
Her uniform is well fittting and she appears at ease; there are none of the usual signs that the photograph was taken in jest. I am convinced she is not in fancy dress although there is no record of any women employed as Special Constables.
My conclusion is that she is an air raid warden but I may be totally wrong.
East Anglia was subject to Zeppelin bombing raids and Norwich was
one of the first cities to be subjected to a 'lighting order' which would be called a blackout in the later war. There were sixty Zeppelin air raid warnings. No bombs fell on the City of Norwich.
My conclusion is based solely upon a comic postcard I have seen of a female Air Raid Warden dressed in this fashion but with a duty band on each upper arm.