If you are a beginner, I suggest you study:

[Taekwondo] (Easy to learn, easy to see the effect, and very fashionable. )

If you want to by going up one flight of stairs, I suggest you study:

[Sanda] You know this without explanation.

[Wing Chun] You know!

[Aikido] Winning by cleverness, similar to Judo and Tai Ji Chuan, is suitable for girls.

[Karate] is a fighting sport with strong fighting consciousness, and all the people I know who learn karate are strong. . . A highly antagonistic fighting sport is not suitable for girls. It's easy to get hurt during training.

[Judo] This is also suitable for girls to practice and fight technically.

[Taekwondo ITF] Taekwondo can be divided into WTF and ITF. WTF is the kind of sport dominated by competition in the Olympic Games, while ITF is a fighting event similar to karate.

[Muay Thai] Personally, I think it's great, but I don't think it's normal for girls to learn this, so I'd better not learn it. . .

You can learn everything, depending on what kind of fighting style you like.