The latest 9.2 PTR build has added many interesting voice over lines for Sylvanas Windrunner, including reflections on her past actions. PATCH 9.2 STORY SPOILERS AND SPECULATION AHEAD! One set of dialogue implies that Sylvanas was not fully in control of herself in the past, but at some point she regained control and saw the flaws in the Jailer's plan.
This led her to fire the arrow at the Jailer at the end of the Sanctum of Domination raid. Edit: an alternate interpretation of this dialogue
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