Before the Great War, the only jobs open to most women were in domestic service. There were some exceptions, for example teaching or some of the professions (for middle-class women) and some mills and factories had always employed women, right from the start of the industrial revolution. Even secretarial and office work was done mainly by men!
The Great War was in many ways a revolution for women in that they had to substitute for men who had joined the services.
After the war, women in general did not want to return to domestic service. With mass production, the period also saw the advent of inexpensive office equipment such as typewriters and adding machines and this sort of work was considered suitable for women to do. Also, many of the men who might have done some of this work had been killed during the war (the Great War killed three times as many servicemen - mainly young men - as were killed in world war 2).
I suggest you also check out organizations such as the Fawcett Society, who have been campaigning for women's equality for 140 years. They have a history section which should prove fruitful.
Well done, Dot, for your pictures!
Could post more...but I've got work to do!