I'm doing a project for our schools's GSA club and part of it deals with gender expression. I wanted to use an example of how expression is influenced by culture by using flappers as an example of early "tomboys" due to their engagement with traditionalaly masculine things at the time (driving, smoking drinking, etc.) Also the flapper ideal of boxy figures short haircuts were an affront to traditional victorian ideals and gender roles at the time.
But the thing is I'm not really sure this is the case as sexual and gender orientation as we know it is new and I'm unsure this was even the case. I asked because if I was wrong I didn't want to be dishonest.
You definitely have the right idea. The roles of women were being challenged during WWI, working in industrial and professional jobs. Which, in a large part, led into the struggle during the 1920s of what was acceptable for women. While the extreme version of the flapper we tend to think of was well beyond what most women would have attempted, elements of that lifestyle permeated regular society. I haven't read any books on the particular subject of Flappers, so I'm loath to recommend any, but there are quite a few on the topic available. "Feminism and the 1920s" would be another good keyword search. This article on the Gender Forum discusses flappers as well as their German counterparts. It would probably be useful to look on either side of the flapper movement as well, understanding where they came from (Suffragettes and feminist movements of the 1910s) and the swing back the other way (1930s feminine form and the Great Depression). It helps to better frame a rather distinct and short fashion.