Queen Tassara is the queen regnant of the (fictional) African nation of Lyrobia. In "Queen for a Day", the girls are sent to protect Queen Tassara after a kidnapping attempt, with an anti-gravity ray, was made on her. Tassara explained that she and the King of a (fictional) neighboring African nation called Kenyopia were to sign a peace treaty that would end a twenty year war between their countries.
After Clover (disguised as the Queen) and Tassara's younger sister, Makeda, are kidnapped, Samantha and Alexandra go to save them along with Tassara. It later turns out that Makeda was behind the whole thing, and that she wanted to prevent her sister from signing the peace treaty. Makeda explained to her sister and the spies that she had a made deal with the commanding general of the Kenyopian military to sell her anti-gravity weapons to them to make sure Kenyopia won the war. If Kenyopia had won the war, Makeda would have been the Queen of both Lyrobia and Kenyopia (implying they were also going to dethrone the current King of Kenyopia).
But Sam, Clover, Alex and Queen Tassara manage to stop Makeda and her henchpeople and have them sent to prison and the spies manage to get Tassara to sign the peace treaty with the King of Kenyopia (the peace conference was in Geneva, Switzerland).