I'm currently doing a 4000 words essay with the title "How do Daisy and Jordan represent the Changing Gender Roles of the 1920s." My main focuses...

It sounds like you have a great start for this essay! Jordan is an excellent example of changing gender roles. She was an unmarried woman and a professional athlete. She definitely broke the mold of gender expectations of the time. 

Fashion—if you are allowed to use the movie as a source in this essay, I think fashion is a good topic for discussion. The flapper style was very popular during the 1920s, the time period in which this novel is set. It was characterized by loosely constructed dresses. This was a departure from the highly constructed and restrictive clothing that came before this trend. It represented women defying convention and becoming more independent. However, it would be difficult to find supporting evidence of fashion if you are only using the book as a source. 

Conspicuous consumption—I am assuming this is dealing with consumption of alcohol? This was during the time of Prohibition, so it was illegal to consume alcohol publicly. I suppose you could argue that when Jordan and Daisy partake of alcohol at Gatsby's parties, they are representing a new social order.  

Another thing to consider is comparing and contrasting the ways in which Daisy and Jordan interact with the world. Daisy is childlike. She speaks like a child, in a breathless, whispering manner. She is not much of a mother—her child is an afterthought. When she talks about her, she tells Nick about what she said to the nurse when her daughter was born:

She told me it was a girl, and so I turned my head away and wept. 'all right,' I said, 'I'm glad it's a girl. And I hope she'll be a fool. That's the best thing a girl can be in this world, a beautiful little fool.

Daisy depends on a man for security. Even though Tom cheats on her and Gatsby promises her the world, she does not have the strength of character to leave Tom. 

By contrast, Jordan makes her way through the world independently. Tom even remarks that her family should not allow her to travel around the country alone. Jordan is a free spirit and makes up her own mind about things. In my opinion, Daisy represents the established order of gender roles, and Jordan represents the changing roles.