From Halopedia, the Halo wiki
Doctor Morgan Rivera was a human scientist of the UNSC Navy in the post-war years.
In 2558, her science team was examining the area where Fireteam Crimson found the Forerunner artifact when they came under attack by Covenant forces. They retreated behind a shield wall until Crimson was able to eliminate all the Covenant forces in the area.
Rivera is voiced by Laura Bailey.