I don't think Melaine actually is a DF (I don't think any of the top WO characters is, for myself), just that her attitude toward the coming of the car'a'carn etc. - for example how reluctant she was to accept changes, is more in line with what I would expect a DF WO to be, ie: no strong enough for what's coming, for what the WO know is coming.

I disagree about Sorilea. She's much too wise, and much too kind, much too interested in others (in a good way) to be a DF. She's an Aiel Cadsuane, and a major strength among the WO - their backbone in many ways. She just doesn't fit the profile. DF are self-serving, greedy, ambitious, deluded and for all their occasional intelligence/cunning (eg: Demandred, Lanfear, Moridin) they are in the end fools. Some like Ingtar are cowards, driven to the Shadow by their fear/despair to lose everything. We have never seen any real DF (ie: not Verin) who can remotely be called "wise", and Sorilea is very wise.

I think most of the DF WO would be taken care of by the testing in Rhuidean (especially the Rings), and the same for the clan chiefs.

If RJ had one DF WO, she might be with Perrin, though I doubt even that.

I'm guessing the closest thing to DF WO we've seen will have been Therava. Corrupted, evil yet not serving the Shadow.