I think she exists in a future where the Traveler has Fallen to the Darkness. There is no more light. However being born of Darkness does not negate her free will or the Exo's primary function, which is to defend the territory of humanity. Using a lost Golden Age ship with an experimental FTL drive modified with Vex technology, she and other resistance members try to undo the key moments in history that lead to the Fall of the Last City. The Vex are pursuing this last glimmer of hope, and indeed are the only Darkness Faction capable of doing so which is why she focuses on them first. That's what she meant when she radios her crew to kill the engines and don't let themselves be found.