Trey aided Romana II after she had returned from the Axis. She stopped Leela and Narvin from returning properly by trapping them in a Chronic Hysteresis. She showed her younger self the results of the Pandora devastation. She offered her Capitol to her previous self, saving her thousands of years in rebuilding the planet. She said that she was the last of her people. She had Romana exiled for the death of Kolspen of Unvoss. This occurred in the Matrix. (AUDIO: Renaissance)
When Romana disappeared, she went with Narvin and Leela to the Archives, where they met Tallan. She helped Narvin and Leela escape the Matrix before it collapsed. Trey later aided her second self in defeating the Daleks, who were invading Gallifrey in her past. She stopped the invasion force from leaving the Matrix by closing it's doors from the inside. She created a plan to trap the Daleks inside the Matrix, thus stopping them from invading Gallifrey itself. (AUDIO: Ascension)
James Goss, creator of this incarnation of Romana, uses the spelling "Trey" for her alias, although the syllable from which the nickname was derived is spelled "tre". (VOR 56)
While in the real world "Trey" is a common term for "three" and nickname for those named with the generational suffix "III" Goss maintains that Trey is not the same Romana III created by Paul Cornell for The Shadows of Avalon, referring to the Cornell character as one among "other future Romanadvoratrelundars". (VOR 56) However, Scott Handcock and Gary Russell have stated that Trey is the third incarnation and was always intended to be, leaving the situation of which post-Ward Romana is the third unclear. 
Trey is the second Time Lord, after the Master as played by Eric Roberts, to be portrayed by an American actor. Unlike Roberts, Juliet Landau plays her role with an English accent.