Sekhmet was the queen of the Osirans.
According to Erimem, Sekhmet lived among Erimem's people when Ra lived among them as a human. Sekhmet was born from Ra's eye to slaughter Ra's enemies. Sekhmet referred to herself as "the eye of Ra". She said that her breath "created the desert" and over it, she sent Sutekh to rule.
Erimem said that killing Ra's enemies gave Sekhmet a taste for blood and she began to kill all life. Ra ordered a high priest at Heliopolis to pour beer that was dyed with the juice of pomegranates as bait for Sekhmet. Sekhmet drank this lake of "blood" and became stupefied by the alcohol. She was trapped in a tomb of salt, or trisilicate, which the Fifth Doctor pointed out was a spaceship which was sent into space. Inside the ship, she was also bound by a blood lock, requiring the blood of four female royals to break.
Her ship eventually crash landed near Mount Megeshra on Peladon. Thousands of years later, a miner broke into the tomb in which she was trapped. Over time she broke the locks, killing Queen Elspera of Peladon, Princess Alixlyr of Mars and Princess Pandora of Earth. She broke the last lock with Erimem's blood, but Erimem had poisoned herself with mandrake. Before Sekhmet could take her dying revenge on those around her, Alixlyr's twin brother, Prince Zixlyr, distracted her by grabbing her still inert form. He activated a Xanthoid volataliser and told the other people there to run. A minute later, the volataliser vaporised Sekhmet and Zixlyr. (AUDIO: The Bride of Peladon)
A contradictory report her talking to the doctor as he ask her for his aid in helping Anubis to ascend.