What a great idea! I know there have been many notable women in agricultural history, but of course my mind is on fall break...
We toured the Cowgirl Hall of Fame during National Convention, you might do searches on some of the honorees (cowgirl.net) for ideas. Also, JoAnn Smith (an honorary member of SA) was the first female president of what is now NCBA. You may have some luck looking under history at some state ag college sites as well. Good luck!
p.s. your question got me thinking: here's something I found searching
http://www.missoulian.com/specials/1.../list/071.html