By 2277, T'Prynn had joined Admiral Spock's cadre of loyal officers and was responsible for carrying out multiple missions for him. In that year, Spock sent her on what she said would be her final mission.
T'Prynn was ordered to contact Captain Zhao Sheng and ask him to rebel against Commodore Diego Reyes. T'Prynn accomplished this by booking passage on the Eighth Happiness and setting the ship up to get intercepted by Zhao's ship, the ISS Endeavour.
After the ship was intercepted, T'Prynn was taken aboard the Endeavour and allowed her to make her offer to Zhao. In return for removing Reyes from the picture, Zhao would receive his honor back, Reyes's command, and the return of his lover. Zhao accepted the offer and led an assault against Imperial Starbase 47 with T'Prynn aboard. (VAN - Mirror Universe short story: "The Black Flag") Afterwards, she would receive a notice of honorable discharge from Starfleet. (TOS - Mirror Universe novel: The Sorrows of Empire)