For now, we can rejoyce that she (and Vhaeraun too!) are alive once more (and that Ed Greenwood is trying to give us more of the Dark Dancer through his novels, even if it is just tidbits of new lore, and that we might know some more about her starting from his next novel after Spellstorm) :
Hi again, all. Irennan, heeeere's Ed:
Communications being what they are in the Realms, with caravans bringing news and gossip and inevitable distortions as things get told and retold, most mortals can't be certain of much; they always have to trust (or not trust) retellings from afar.
However, the word spreading about the return of Eilistraee and Vhaeraun comes from excited reports of mortal worshippers personally meeting MANIFESTATIONS and AVATARS of the deities; i.e. yes, Vhaeraun and Eilistraee are both "back."
Now, as to whether they'll appear face to face with a given mortal in a given location in the Realms, that's a far different matter. The gods in general seem more "distant" post-Sundering, more "heard from" than "personally seen."
And there you have it.
The Word of Ed, so to speak.