What is the Sharee’ah ruling on a girl who learned taekwondo?

All perfect praise be to Allah, the Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.

Practicing sports is a legitimate right of both males and females as long as the ordinances of Allah Almighty are not violated, as when a woman indecently appears before men, neglects some of her husband or children's rights, or when a sport is men-specific. The sport under question is specific to men as it depends on making many movements and physical strength. This is specific to men rather than women. In this respect, it was narrated on the authority of Ibn ‘Abbaas that he said, "The Messenger of Allah, sallallaahu ‘alayhi wa sallam, cursed men who imitate women and women who imitate men." [Al-Bukhari]

In Riyadh As-Saliheen, An-Nawawi mentioned this Hadeeth under a chapter entitled "Prohibition of men imitating women and women imitating men in dress, movement, etc."

It is better for the Muslim women to play as much sports as is enough to help her carry out her daily duties, such as walking, running, and other sports, while observing the relevant Sharee'ah regulations. It should also be known that violent sports may cause women to lose many aspects of their femininity.

Allah knows best.