First female Judo students started to train in Kodokan in late years of 19th century.
First Kodokan female student was Sueko Ashiya in 1893 and joshi-bu (woman's section) of Kodokan was open in 1926. One of Dr. Kano female students at Kodokan was Keiko Fukuda. The highest ever ranked female in Judo hierarchy (born 1913 she's 9th dan from Kodokan and 10th dan from USA Judo Federation as of 2012) and last surviving student of Dr. Kano. Keiko was personally accepted by Dr. Kano as a token of appreciation for her grandfather - Fukuda Hachinosuke, the headmaster of Tenjin Shinyo ryu school of jujitsu, who was the first jujutsu teacher of Dr. Kano.
In all this, woman and woman images presented promptly in Kodokan early promotional materials (to highlight even more Judo "gentle" superiority over brutal physical force). In Kodokan women participated in self-defense and kata training. Woman kata training there was on even more advanced schedule then man's (Ju-No-Kata as an example), but I don't know if women took part in shai competitions. Anyway, women Judo World championships started only in 1980.
Even some female sport competitors can be on an equal footing with their male counterparts (in Judo Rena "Rusty" Kanokogi in deed made this mark in 1959) in general female athletes compete within there own gender group. Even more, in the later years female gender validation (based on hormonal composition) became a sour point in sport of high achievement (track-n'-field in particular). Those are good reasons for it - as in the sport that is about of "fair competition" masculine body build and hormonal structure has natural, and hard to compensate, physical advantage over female. This biological physical gender "inequality" is a build-in property of us, as Human species (not all living species have such notable gender differences, and in some species females are physically superior to their male counterparts).
I had a chance to be a training partner for couple of world-class female judokas in mid 1980th (as Women Judo championships started in 1980 Soviet Union sport administration saw it as a priority not to be "left behind" and finally permitted female training in traditionally conservative male-only Soviet sport SAMBO and Judo). Those girls' international ranking was head-n'-shoulders well above mine and I was two or three weight categories lighter... Well, two cases is not representative statistic by any means, but those two well-ranking female judokas ware absolutely no match to me or to any mid-ranking-and-above guys in my team (actually my coach choose me for this task because I displayed the most restrained behavior among my teammates).
Well, when I do not enjoy watching girls beating each-other in octagon, on a boxing ring, or even on tatami (hay, it's a free country and I have full rights not to like any spectacular sport; so, don't call me "chauvinist" for this, I also don't like watching football, baseball, water polo, pro-wrestling, and any kinds of MMA fights :) woman Judo training has it full rights and rich history. However, I do have concerns with female sport Judo as it comes to self-defense because of specifics of woman self-defense training. Success in women Judo tournaments can develop overconfidence and wrong response reflexes as female body muscular structure and weight distribution are different from male (and male attacker is much more likely, even not only, scenario in real-life self-defense situation facing any woman). So, it must be complemented by proper 80/20 self-defense training. As for general fitness, sport Judo is as good as field-n'-track, sport games, or any other sport activity.