I just caught up with the full comic, and decided to see what the forum said about some things.
Read this thread, and decided that it can't hurt to toss in my own theory.
There's some logical chaining here, so I'll put up the data I saw that convinces me of my theory.
1) Sadako taught Lia about the Dream world. A lot about the dream world. Enough that a book written by her was sufficient to get Fiona back inside.
2) Sadako held Lia's conscience deliberately. Given her position, we can be fairly certain she knew what would likely occur.
3) When Lia was caught, Sadako initially wanted to fight her. Clearly, that was planned, and she expected Lia to be in a mindset where they would fight.
4) My reading of the Fiona's Coma Dream sequence is that Sadako wanted Lia to fall for Fiona, and vice versa - there seems every evidence that Sadako threatened Lia's Conscience to make her change her attitude on that very subject.
My theory: Sadako is tired of ruling the place, and wants a successor. I expect her bit as George was an attempt to eventually bring Lia around peacefully, but it fell through. So she decided to make Lia into someone who could kill. That, too, fell through.
The Fiona's Coma dream can be viewed in one of two ways. First, an attempt to make Lia angry enough to fight Sadako, or, alternately, an attempt to groom Fiona for the position she'd originally intended for Lia.
1) Sadako banned Fiona from the dream world, but, Someone made sure that Fiona found the dream book.
I think that someone was Sadako herself, doing her best to make Fiona angry enough to join the DWLF and do some damage. Again, notice how Fiona's conscience was taken, practically guaranteeing that she'd become unhinged. Of course, Fiona, like Lia before her, doesn't react quite as expected, and goes haring off after Lia.
So, another change in plans. Make sure to get a diary of Lia's movements into Fiona's hands. Get them together. Maybe, comparing notes, one of them will get angry enough to do what must be done.
Why must it be done? That's a question. Clearly people can be killed in the Dream World - but can they suicide? Maybe suicide isn't in Sadako's nature, maybe the position has to be taken by force?
Of course, this is all pure speculation, but from what I've seen, at least parts of it fit the facts, and none of it contradicts what we know - so far. At least, not that I can see.