This is also dovetailed with the revelation in "Before the Storm" that the Forsaken are pressured (sometimes strongly) to break away from their pre-undead lives and assume entirely new identities as Forsaken to separate themselves from who they once were. This is taken as far as assuming entirely new names like Velcinda did in an attempt to be someone entirely else in undeath than they were in life. The Forsaken truly seem to operate as a cult of sorts, with Sylvanas at its head as the source of all direction and culture. Before "Before the Storm" I always considered the flow of power as deriving from the Forsaken and moving upward to Sylvanas, with Sylvanas at the center of a cult of personality more or less created by her followers (those she freed from the yoke of the Scourge). But more and more it seems that Sylvanas has deftly manipulated her original support she would've had in the early days of the Forsaken to create said cult of personality - engineering their society and culture to lionize herself, and slowly and surely eroding the Forsaken's self-sufficiency and making them dependent on her in every way.
This is possibly a change in the society post-WotLK, stemming from the traumas she suffered and the change in her worldview following "Edge of Night." But this kind of social change seems like it would take longer to bring about than just that, all considered.
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The morality of her actions? No, probably not - she personally still doesn't know who is or isn't legitimately defecting (she says so in the text itself), meaning she was still acting on essential paranoia or the mere suspicion of treachery. Does it justify them? Well, perhaps more than otherwise, yes. If the Desolate Council at large were traitors and Elsie an unfortunate element of collateral damage then Sylvanas' actions aren't quite so beyond the pale from the objective standpoint - few leaders would permit figures high in the government of their coalition to freely defect to an enemy state without consequence. The fact that she doesn't know (or seemingly care) who is or isn't guilty before executing them is the moral quandary here, not the substance of those actions as concerns potential treason.