Clamping both together since it's the same answer: in Before the Storm, the Naaru Saa'ra who Calia constantly meets in her dreams nags her with - I found - borderline manipulating tactics to prepare her for the service she'll do for the Light, so that she could be freed from the terrors still haunting her since the Lordaeron undead invasion.
Now for a quick "Light and its agenda" tangent:
Anduin of course does not want Calia to participate in such a delicate meeting.
The situation is tense, a war is brewing, there's unresolved conflict from what went down in Stormheim, and in such a landscape the last thing this meeting needs is for the heir of the previous royal family to be present, more so if it bears the same name of Sylvanas' butcher and tormentor.
Or at least her first tormentor.
Anyway, Anduin's stance changes the moment the Light ensures him it would be ok. His mind however keeps telling him this is wrong. And for good reason.
So then Calia participates in the meeting, reveals herself, Sylvanas opts for eliminating her and shoots an arrow, Calia's Power Word: Shield vanishes right before the arrow strikes her and the arrow kills the Menethil.
Anduin then performs the resurrection, but the Light takes over and Calia returns "as the Light and she herself would have her be", quoting Saa'ra.
Here we get two most interesting parts:
One, Calia would not have wanted to be any sauce of undeath any day of the week. In BfA she rejects the Menethil name, and throughout the novel she gets flashbacks of undead claws tearing at her.
Two, the nature of Calia's undeath has nothing of the tormenting nature that bounds the Forsaken because the source is different.
"Anduin watched as everyone responded to Calia’s—what? Resurrection? No, she was still dead. Dark gift? That wouldn’t be accurate either, because it was the Light that had been present today. There was nothing of darkness in this undead woman."