If you were to read her Grimoir card, it states this; [spoiler] "Stories of an Exo who walks in the Darkness without a Ghost have long haunted the Tower. Legends say this anomaly dissolves in and out of the world, intangible and elusive, as if she is a visitor from somewhere beyond."[/spoiler] meaning she is some form of a physical appearence, however she was not forged in light. The card then goes on to state; [spoiler] "Some believe she's the last of an ancient Exo squadron, fighting a long-forgotten war. Others dismiss her as a hallucination caused by exposure to Vex technology. But there are those who maintain that her intervention saved their lives - or averted unspeakable catastrophes." [/spoiler] And the gun she has is called the [spoiler]Stranger's Rifle[/spoiler] and it's description says that [spoiler]It has parts that should not exist yet[/spoiler] meaning that she [spoiler] might be from a time in the future [/spoiler] which would explain her intervention on the Moon, Venus, and her watching your Guardian from a distance calling you "interesting, but not entirely interesting." Hope this helped... and the Spoilers are there for a reason.