Osloo was the Presidenta of the planet Capron. Osloo took over after she had her husband (the king) arrested and taken to the slave mines. She said that her stepson, Commander Ezz, was a traitor. When she discovered the Sixth Doctor's TARDIS, she tried to use it to invade the Earth thinking that their defences were weakened fighting World War II. When Peri Brown tried to warn Osloo of the dangers of her slave mines, she threw her in jail.
When she learned the truth about the Doctor and Peri's origins, she attempted to force the Doctor to serve her in her plans to conquer Earth, but after the Doctor took Osloo to Earth and back, he deliberately failed to adjust the dimensional settings when taking Osloo back to her dimension, resulting in Osloo regressing back to her infant state, giving Ezz the chance to retake the presidency. (AUDIO: The Macros)