Known spawn locations (click for map image) for your "neriakd.txt" map file (note for all known Neriak Fourth Gate named spawn locations, see this quest entry):
P -523.8600, -897.5700, 14.8600, 127, 0, 0, 1, Archon_Kela_G`Noir
P -466.1900, -982.1800, 14.7500, 127, 0, 0, 1, Archon_Kela_G`Noir
P -535.2400, -913.7000, 14.4500, 127, 0, 0, 1, Archon_Kela_G`Noir
P -635.3414, -815.7947, 12.5040, 127, 0, 0, 1, Archon_Kela_G`Noir_(roam)
One of the maps seems to show her spawning in same room as Arch Lich Lyra. Actually the Archon spawns on the next floor UP. Placeholder is supposed to be a dark mender altho I found her up when I zoned in.