She obviously knew about the plague being developed, but they sorta changed it (what was the original lore?) to Putress being the inventor.
She wouldn’t have minded the collateral damage if it meant killing Arthas. But she didn’t intend for it to be used against the living. Using it the way Putress did screwed her over.
One commenter said this “marries” the cinematic with what Afrasiabi said. I’m okay with it.
I still don’t get the logic for the sludge fields, blighting of gilneas, teldrassil, darkshore, her alliance with helya, the need for the lantern and her deception to Saurfang.
Sludge fields: Rebel forsaken wanted to make his own undead army. Originally the place was for growing mushrooms and things for the blight. Sylvanas ordered the Warden’s death after learning.
Blighting of Gilneas: Varian sent an army to destroy the forsaken and take Lordaeron (Syvanas foresaw this when she died). Blighting them was the best way to destroy that army with minimal losses.
Teldrassil and Darkshore: More souls to empower the Maw simple as that.
Alliance with Helya: Jailer wanted the powerful Valks of Odyn.
The lore from Vanilla was that Sylvanas ordered the RAS to develop a “new plague” to be used against the scourge (and maybe even the living in the long term).
Sylvanas is full on nihilistic by the time of WoT and is all in on sending souls to the Maw.
The soulcage was intended to be used to take souls from Odyn and send them to the Maw.
Sylvanas actually wanted Saurfang to join her on her plan, and asks him questions relating to changing fate and how he feels about what happened to his son. He says that no one should have the power to do that, so Sylvanas changes her mind about letting him know the true plan.