Follows some precedence from Asian cinema where strong female characters capable of martial arts acting medieval times have been inserted usually in the form of a peasant or servant girl, concubine or princess (usually one of those).
In the Netflix series "Marco Polo" the strongest female lead was a Chinese concubine of a Mongol warlord who was also the most feared assassin in all of China. This was later tried again in casting for the current Shogun series where a servant girl was tasked with assassination of John Blackthorne had skills to take out 10 fully trained samurai.