Here are some other candidates to be on the $20 bill, or other units of currency (almost all are Americans)
Edith Clarke, mathematician, pioneer in electrical power
Cecillia Payne, discovered how stars work
Annie Bell, compiled data for Cecillia Payne
Marie Tharp, proved continental drift
Rosalind Franklin, x-ray crystalography critical to discovery of DNA
Grace Hopper, inventor of COBOL, computer science pioneer
Radia Perlman, RSTP, etc., "The mother of the Internet"
Bella Abzug, Mayor of New York
Golda Meir, 4th prime minister of Israel
Catherine the Great, architect of Modern Russia
Marie Curie, discoverer of radioactivity
Lise Meitner, first to explain nuclear fission, 109th element "Meitnerium", director at Kaiser Wilhelm Institute
Murasaki Shikibu, authoress of the world's oldest novel, The Tale of Genji
So, for starters, the Internet, the world's most popular computing language (through the 90s anyway), some of the most important phenomena that make our world work which we didn't understand AT ALL before: continental drift, that stars are made of mostly hydrogen, how they work, etc., what radioactivity is, how nuclear fission works, and what DNA is and how it's structured, and don't let's forget transmitting power over long distances with electricity, among many other things, were ALL the accomplishments of WOMEN.
I wrote another little piece on great women of our time.