I believe that Queen Nelis revives people the same way Luca does. Being a powerful enough psy to use multiple elements, Nelis should be able to learn Soul Suck. To get Soul Charges, she would have to kill someone with Soul Suck. If she depends on her supply of Soul Charges to resurrect the dead, then that would explain why the Queen "won't raise the dead for just anyone." She also requires the corpse of the fallen in order to revive them. If a body is completly destroyed or it can't be recovered, the person in unable to revived.
I completely disagree on both counts, especially in light of what I've written in my last posts in the
Noctus still alive? thread with regards to the need for the body for the person to be revived. The fact that Nelis "won't raise the dead just for anyone" indicates more that she can't be asked to waste her time for those who are not important for her plans. The fact that Gen. Darkeye cannot die (again, speculation, including suicide, on the first page of the Noctus thread) and that fate itself, rather than Nelis, revive the Main, indicates that there is much more to it than just a body or lack thereof. Look at the attacks that kill teammates: sometimes they get killed by a Mind Blast, and that leaves essentially no marks on the body, or they can be burned by Fire Breath or sliced up by Spin Saw, yet all can be revived, though in some cases the bodies are mutilated or lost (Nelis can revive teammates who were lost over water in Lake Alto battles- and given that a lot of them die mid-battle, no teammate has time to go and collect the bodies, especially if only the Main remains alive). Then again, fate revives the Main, even if he's killed right in front of Tastidian by Flavin or Vagrant.
For the way Nelis revives beings, I think that her method is very different to the one used by Luca- she doesn't need a soul charge (ie a walking stick) for her to perform the act, as she is a very very poweful Psy, whilst Luca is not that powerful, but, rather, can perform such tasks due to her nature of being a spirit, whilst Nelis was very much a living being (hence, Luca even operates from a/via a different plane, since she isn't fully in the material plane, like Nelis was).
For the points mentioned by Ertxiem:
1). Estimating the time taken for the Main and the teammates to reach HQ after each battle (and taking into account that teammates could've died in the first battle, without the Main returning to Somnus), guesstimating distances from the map, I'd say that at least several days can pass and Nelis can revive beings (that applies to all races which were represented by the teammates). Potentially, the time can be greater, but that's the minimum time.
2). Given that, as noted in this post above, some of the bodies are lost or highly mutilated, whilst others are completely undamaged (think of a teammated getting damage solely through Mind Blast), Nelis can revive all, without exception, which makes me think that the resurrection process is linked to the soul and that all beings have a soul (judging from Luca's ability to use Soul Suck on all enemies, unless they have mental immunity).
3). It looks like this is important: from my thoughts in the Noctus thread, it would seem that Gen. Darkeye couldn't simply commit suicide in order to get saved from the advancing Spriggats and more conventional means had to be used. Possibly, if a person dies willingly, then their soul is transported to the "other plane" so fast that Nelis cannot retrieve it back, but if a person is killed, the soul doesn't quite feel at peace and lingers a bit more in this world (and, if the will is strong enough to stay in the material plane, then the result is the soul taking on a spirit form), then Nelis is able to re-call it back.
4). Very difficult to call that one: either way, even if one soul is easier to revive than another, it looks like the power required to do that was negligent with respect to Nelis' Psy powers, hence she could revive beings of different races almost at will.