Do you understand how long people have been asking for undead elves? As long if not longer than High Elves.
And if after Shadowlands we learn Calia has been using S'era to spam resurrect people to save them from the Maw as forsaken, that would make sense & justify why she came to the Shadowlands at all. If she was privy to that info in the time before they appointed the new Arbiter, this would make the most logical sense & would be her moral imperative to ressurect as many people as possible since that seemed to be one of the few ways to save people from the Maw.