Most martial arts in Japan are largely populated by males, however women are rarely discouraged from joining and in fact many are glad to teach and learn alongside women.

Cravez wrote:

QUOTE:
While girls can do many martial arts, I think there is a traditional connection with girls to do So(u)jutsu (Spear Fighting/Training) and may be popular with girls. Judo tends to be another popular martial art amongst females.

I believe you may be confusing sojutsu with naginatajutsu, the art of the glaive. If anything, sojutsu is historically associated with sohei, the famous/infamous warrior buddhist monks. While the naginata predicated the spear, the prestige of the monk's weapon eventually trickled into the mainstream and the spear became popular by the warring states period. Naginata stuck around, but became increasingly associated with women in the samurai caste. The Empire of Japan made naginata compulsory education for girls and young women, leading to the standardization that birthed modern naginata. Today, atarashii naginata is a sport populated almost entirely by women, although it is remarkably divorced from anything found in the koryu naginata schools.

Aside from the aforementioned judo and naginata, karate, shorinji kenpo, kendo, aikido, and kyudo come to mind as modern martial arts with women in larger numbers. It's not unusual for them to be in the minority, but don't let that discourage you.

AzoraNHK wrote:

QUOTE:
in my opinion, ii guess it's normal for me because the world has changed. Women need something to protect themselves. Pepperspray sometimes does not come in handy esp when you forget to bring it. Thus, body as a form of weapon is a good choice for protection.

have a reason why you take martial art in the first place.
and "NEVER GIVE UP".

There is a fine distinction between typical gendai budo and training to deal with assault. Something like judo is tangential, however not specifically tailored to the needs of someone who explicitly wants to address violence in their life. Modern budo strive for greater self-improvement through excellence in their arts. These budo are increasingly sportive, and while the randori of judo is still among the most rigorous exercises in grappling available, it just doesn't offer or claim to offer what a say, dedicated women's self-defense course can in terms of educating you about avoiding and escaping violence.