Predictions
Sylvanas makes a token effort and tricks the Jailer into giving her soul back which was part of her big plan. It also causes him to leave her behind so she can tell everyone his weaknesses, plans and location of his next target.
She did not properly mind control Anduin and left room for him to regain control at the right moment. He is a shadow agent following the Jailer.
This’ll probably happen. Anything to give Sylvanas her precious redemption arc, no matter how nonsensical it is.
She’s been planning this moment - this exact outcome - since before Wrath.
There’s galactic brain, and then there’s Sylvanas.
I always knew that Sylvanas was the only character to regularly read WoWpedia but I didn’t think she’d also be the only character to actually be on the writing team
She knew the jailer wouldn’t killer her and just give her her soul back. Truly a 10D chess master.
We didn’t see what happened to him when she was holding the mourneblade to his neck for a reason. Now I’m really disappointed this is probably why…
I’m going to say that this wasn’t a trick. I think her plan A was for Zovaal to just give her soul fragment back after they won; and he did it anyway even though she turned on him.
This was her plan B. I think Sylvanas just gave him that armor, but found a way to weaken it so Anduin could have moments of control, if the Jailer turned out to be a douche.
Ah, I see.
Slyvanas knows she cannot take down the Jailer alone, and she has no army. Helping the Heroes weaken Zovaal gives her her chance to claim the Throne for herself!
Slyvanas, I should have never doubted you MA QUEEN!!! 
Shame that. If only she had a leadership position to have one.
She had to play the part to get her soul back from Zovaal, he would’ve destroyed it before she had the chance to reclaim it by force. All part of the plan…
She’s waiting patiently, for the perfect opportunity to strike, when Zovaal is at 4% and only 6 remain alive in your raid!