When Monique arrive Sonja is already 3/4 in the floor, the scholar have barely the time to say her piece before the ghost fully disappear, without a sound, Rousseau is probably used to it.
But lack of reply doesnt mean lack of attention, Sonja is still there, somewhere and the first to notice it is the man who dared speak ill of the book giver, anyone adding quality material to the archives automatically get a better treatment, our Banshee wouldnt have much to protect...and read... if people like Monique didnt add new texts.
The more perceptive may notice a shadow, briefly moving in an unnatural way, for a shadow, it caress the back of the fancy-pants man , who shiver and lose the grip of his cup, spilling the content.
After that, nothing happen for several seconds, no sight of the ghost.
Later, when a group is being forming around the scholar, discussing ideas and tactics, Sonja approach, unseen but heard, oh yes, Garrak, Thrack, Yaronvael, Nemeia and Monique herself can hear a quiet but perceptible laughter from...seem the tavern itself.
"you all will dieeeee" a whisper, Sonja speaking with very low voice, barely audible by the five of them.
Slowly a light form on the the table used by the 5 adventurers, an illusion that doesnt even try hard to fool their eyes, it evolve and take the shape of a beholder, the size of a basketball, the illusionary creature look toward them, opening it's mouth while lightnings appear behind it's image.
A diversion!
While all of this is happening, Sonja descend from the ceiling, right on top of the tallest among them( currently garrak?) upside down, silent as always, with an arm outstretched and a closed hand with only the index finger pointing out, until it make contact with the gnoll's head. Nothing happen , expect the gnoll having a ghost finder inside his head, by this point Sonja has been spotted.
She whisper, again.
"Ground dwellers, what makes you think their lair is made for your kind? that they will fight you on your terms? you'll be climbing, leaping or using magic to travel in what probably resemble an ant nest with a lot of vertical mine shaft against a foe who doesnt even know how -walking- feel" the illusionary beholder float in place while Sonja withdraw back into the ceiling, only to reappear from Yaronvael own shadow, this time standing upright and at her usual floating height, a few inches above ground.
The illusion change and now it look like a caricature of Garrak, flying superman-like down a well, only for a beholder to look at him, the caricature fall and fall and fall, until it splat on the illusionary ground, the splatter details are a bit macabre.
"They know the territory, they outsmart you, they expect you, they had time to prepare... " she keep talking with low voice.
"And" she say, shifting her attention on Thrack, her voice raise to a normal tone and become cold, analytical "their skin is as hard as steel, but maybe it wont make a difference for someone with your powerful body" The illusion end and Sonja just float there, outside the archives she feel like a fish out of water, social interaction with so many living creatures make the ghost nervous .
While Monique know what she know because she's a brilliant mind, Sonja knowledge come from time, centuries spent reading books day and night.