But who is this?
Her name is Vanth and she is another Etruscan chthonic god depicted as a demon and she adorns funerary art.
What is their relationship other than the obvious historical one?
Well I also read a lot of science blogs and this picture of the largest trans-Neptunian objects came up (in a discussion of the Oort cloud.)
Vanth is the moon of Orcus.
I can't even begin to tell you how many ideas came flooding in on that one!
Vanth orbits Orcus in a tight precise circle and they are tidal locked. Vanth is never far from Orcus then and she always keeps her face toward her master.
Mythological Vanth shares a role similar to that of Charon. She brings the souls of departed to the underworld. She has a torch to light her way, a key to unlock the gates of the underworld, a scroll with the information on the deceased and a sword. According to myth Vanth appears as woman, much like an Erinyes and described as young and vibrant.
There is a Pathfinder creature called a Vanth, but it lacks some of the charm of this demon.
No I think I prefer Vanth to be a vassal of Orcus. Responsible for bringing him the choicest souls to be corrupted into foul undead. In truth that picture of Orcus above should be reversed, Vanth (the woman) should be the one presenting the skeleton to her lord.
It could be that this unique Vanth has many of the lesser vanths at her disposal. Maybe the souls her lord rejects become part of her own army.
I also saw this picture of Stephanie vanRijn that had me thinking of the relationship between Thanatos and Eros. Maybe this what Vanth looks like to humans.
Hit Dice: 11+15** (70 hp)
Armor Class: 1 
Attacks: 1 sword (1d10+4)
Special: Flight, Magic resistance (55%), regenerate (3 hp/round), +2 or better weapons to hit.
Move: 24' / 60'
Save: F12 (Basic) 12 (S&W)
Alignment: Chaotic Evil
I will have to develop here more later.