Um she wasn’t mind controlled Moontear. The jailer had lied to her from the beginning.
Like when she said she could convince Anduin to join them willingly and the Jailer said OK. Did he talk to himself? or what?
Same thing that she tried to convince Anduin with the same lie which she didn’t know was a lie but she failed. Because Anduin could see through the lie, and tried to convince her instead to betray the Jailer. But the banshee queen side of Sylvanas stepped in and stopped her. Anduin almost had her on his side.
Which is why jailer didn’t tell Sylvanas that he had an armor made for Anduin to control Anduin.
At the end of the raid Sylvanas realized she had been lied to all this time. She been serving the same master over and over again. Its why she heard Arthas voice, then Lich King voice and then Jailer again.
Sylvanas thought the Jailer would help her break the cycle of death so She could never die and no one could control her fate.
The Jailer feed her with lies and empty promises, He gave her a purpose and a belief and used her as a pawn.
The burning of Teldrassil. The jailer needed more souls in order to break free from his prison. And feed her with a lie that once the cycle of death is destroyed, those souls would live again so She believed it wouldn’t matter.
Well her first plan was to take Stormwind and kill everyone there but it was too well fortified, so they went for Darnassus instead and She told the other Horde leaders the plan was to capture Teldrassil and not destroy. That’s why other horde leaders looked surprised when she said “Burn it”. Even Nathanos was surprised. And when Delaryn Summermoon said “I grief for you, you made life your enemy. And that is a war you never win”. And most likely Sylvanas could see herself in Delaryn Summermoon, “You can kill us but you can never kill hope”. and that’s the same situation as with Anduin. If Delaryn Summermoon could let go of hope Sylvanas could to. then the Banshee Sylvanas remembers why they were doing all this for and tells the other horde leaders to “Burn It”. Even if that was Sylvanas plan all along.
Even in the comic Sisters reunion, Sylvanas plan was to kill her sisters and raise them as undead. But at the very end She never gave the order to attack and her dark rangers were confused. I think She was hearing herself, the Ranger-General Sylvanas.
And I think if we see Arthas again and we get to learn his story. He was never mind controlled either. He was just feed with lies just like Sylvanas.
Deceptively Cunning indeed.