The lady on the left there (Cynthia, by William Strang, 1917) is a long way from the bobbed hair of the 20s, (which was first recorded in Chelsea in 1914). But in the East End of Glasgow, in 1919, 1920, I think a young-ish woman would have looked more like this, (though Strang, who died in 1921, may have been looking back to the previous century). All the same, when the lassies started getting their hair cut short in the middle of the 20s, must have been quite something, especially if they were applying lipstick and smoking cigarettes out of doors.
The pace of change must've been dizzying to someone who'd grown up in the Edwardian era, been through the War, and then, pow! The 20s!