She wanted his position, had more power than we realized at that point and was right there. Instead of the master she is playing at serving doing the dirty work I could easily see her doing so more easily being right there.
Later on she barely feigns surprise at Vol’jin nominating her as he closes upon death.
She convinced Arthas to take up Froutmourne in the the first place and if you squint really, really hard, you can see her in the background of that scene when Reforged comes out.
At this point probably. Sylvanas is responsible for every bad thing ever in the Warcraft universe. She actually planned to powerslide into frostbourne because she knew Arthas would give her the banshee powers she has now and allow her to communicate with the Jailer.
I’ve long said she probably provided the poison, regardless of if one looks like an ink stain and the other is spread out through the body’s veins. Vol’jin was stabbed deeper than Genn was shot. Genn also immediately got medical treatment.
Poison was probably meant for other Horde Leaders so that she could become Warchief without other Horde Leaders scrutinizing her. The Jailer of course decided to make her Warchief immediately without easing her into the spot comfortably.
She’d much rather have had Thrall, Baine, Saurfang, Lorthemar and Rokhan all die first before Vol’jin appointed her as Warchief so not to deal with the hassle of rebellions… The Jailer of course was impatient.
This line from BtS posted puts things into perspective:
She laughed sharply and without humor. “Baine and Saurfang and the others say I have not been giving them enough attention. My people say I have been giving them too much. Whatever I do, someone objects. How can anyone rule like this?” She shook her pale head. “A curse upon Vol’jin and his loa. I should have stayed in the shadows, where I could be effective without being interrogated.”
Where I could do as I truly wished.
The italics were her inner thoughts while her words before that was out loud and heard by the public.
If Blizzard’s words are true then Sylvanas knew her Boss was responsible for her position yet was not happy about it. More dialogue in BtS shows that she felt sorry for Vol’jin which probably makes her team-up with the Jailer more strained.
Now did she kill Vol’jin or did a Felguard do it: https://us.forums.blizzard.com/en/wow/t/did-anyone-notice-this-in-the-wisdom-of-a-warchief-questline/114691 suggests that Sylvanas was actually aiming at Vol’jin when the Felguard stabbed him.
Of course she may have hesitated forcing the Jailer’s hand. Alas we don’t know enough to know whether or not she actually took the shot just that she felt sorry for the death of one whom she respected.
Honestly BtS should have foreshadowed everything better by having her inner thoughts curse the Jailer after publicly cursing the Loa but Blizzard just wanted to hide the Jailer’s existence(which the Three Sisters Comic showed was already in the plans) until the Shadowlands reveal!
“We’re not saying one way or another,” Danuser said. “We want you to see how the story plays out in the chapters to come. Sylvanas has certainly had an interesting history, and looking back at the choices she made is something we want the players to look back at and revisit.”
It’s another example of Blizzard answering a question in a wishy-washy way that allows them just enough wiggle-room to do whatever it is they want to do. The thing is that a lot of these things take on a life of their own and reach almost mythical proportions in the community.
When Afrasiabi mentioned the Wrathgate for a lot of people suddenly it became canon that Blizzard confirmed Sylvanas ordered the incident at the Wrathgate…even though it is not at all clear that it is what Afrasiabi said.
Another example is the faction merge which took on a life of its own in the community based on some vague off-the-cuff throw-away comments from Blizzard that got blown way out of proportion and just spread like wildfire. Or that Afrasiabi promised that the Azshara cannon would be fired in BfA…when he clearly meant it would be fired at some indeterminate time in the future and that the thought had not even crossed his mind until that question was asked so obviously it was not planned for BfA.
Almost all of these can be traced back to click-bait Youtubers.