IF you think like T&FN's world rankings committee (and that's a big if) then you can't rank Flojo #1 in the 100. They say time and time again that one race does not make a whole season, no matter how good it was. In a career mindset, then, one season does not make a whole career. Of course, if you're looking at how dominant someone was at their peak, it's hard to top Flojo.
You missed someone in the 100 -- Helen Stephens. She had an undefeated career. She never lost to Stella Walsh, and that's a "woman" we know for sure wasn't a woman.