Darth Zannah is definitely not the only female Sith lord in the history of Galaxy, but instead, there existed many female Sith Lords and apprentices in the Star Wars universe, including Asajj Ventress, Lumiya, Darth Talon, Darth Traya, etc., demonstrating the fact that gender does not determine one’s ability to harness the Dark Side of the Force and become a powerful Sith.