Y'know, there's a theory that Darklurker is another, more powerful fragment of Manus and thus is stronger than Nashandra. Though, I wonder if the Throne Watcher and Throne Defender are also shards opposed to Nashandra, since the Darklurker seems content to sit in the Abyss if it is another piece of Manus.
Yeah, Elana the Squalid Queen. They're under the impression that for Crown of the Old Iron King it's going to be Nadalia, the Bride of Ash. Mostly, the interpretation is that Nadalia was the Iron King's unnamed wife that competed for his affection over Mytha.
The Darklurker may be a shard of Manus...Or maybe it's something else that lived in the abyss. One thing is for certain though, Elana, the Squalid Queen(from the DLC) is another shard of Manus. Well, it's not 100% certain, but she is referred to as "the Child of Dark", so it's highly likely. And I personally think the Defender and Watcher were supposed keep Nashandra(or anyone for that matter) from getting to the throne. I mean, it's pretty obvious Vendrick figured you what she truly was at some point, and that's why fled to the Crypt and commanded the two to guard the throne.
It's mostly speculation, though. I guess we may never know the ultimate truth about...Well, most things in the Dark Souls universe.
From what I understand, Elana was actually cut content made into a boss. If the DLC (as in all three episodes) is focusing on the Shards of Manus, then we have at least two more that we will have to deal with in the form of Alsanna, the Silent Oracle and Nadalia the Bride of Ash. Elana creeped me out as it was, so I can't imagine what the other two look like or fight like, though I am hoping they're not reskins of Nashandra.
In any event, I am hoping the Old Iron King DLC focuses on the Keep before it sunk into lava. Hopefully dealing with the relationship between the King, Mytha, and the unnamed... Oh God... If the Iron Crown deals with Nadalia (the name fits) then I am honestly fearful because it's going to be rather crazy fighting someone who can potentially summon another boss to help her like Elana did with Velstadt.
That's my favorite thing about the lore, it makes it so that we can make the story how we want to.