When we first saw this mysterious guardian in the very first mission I though that she would help us later on. However, later on during the first moon mission we see her face and because of the cloak I'm guessing she was a hunter. In the scene that we see her she seems more like a ominous threat. Why else would she let us to fend off the hive horde alone.
My theory is she used to be a guardian like us but then her ghost died, and she went rogue trying to steal other guardians light, and become the traveler's worst enemy yet.
I don't know but I wanna know. any thoughts, theories.
-
Operating under the assumption that Exos are ageless and only die from getting killed. The stranger is the last surviving Guardian of the Golden age, the only thing that was actually THERE when the Darkness came, she fought and survived in the wild, away from the devastation that the Darkness brought. Even the speaker doesn't know the details of the collapse. The reason this Guardian has no ghost is that she never died and resurrected like the rest.