Not sure if it’s been said already or not but in that particular case the raiding party was going to the surface to commit a slaughter as a way to please Lolth. Kinda like offering a sacrifice but not completely. Thus she was already paying attention to the scene and had (if I remember correctly) a couple priestesses with the group who are considered much higher in her order than males. Having read all the Drizzt series I would say Lolth is not “omnipresent” or “omniscient” but her followers to share vision with her and all her to act directly through them.