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.