But she obviously faced one of the Forsaken (Moghedien) once. She knows about Shadowspawn. We already learned about the limits of knowledge through Aginor - he knew how to use tech to make Shadowspawn, but could do none of that once they lost the infrastructure for his experiments. He knew how to use the tools of his time, not how to make them from scratch like some WoT MacGyver...

Look at what Rand learned when he saw through his ancestors' eyes: Aiel were once like the Tinkers; they had planes; Lanfear was a good but damaged woman who found the DO in an experiment to find a power that men and women could tap; Avendesora was in every town; Ogier, Aiel, and Green Men protected crops through singing a Song. This is all stuff that apparently no one but Aiel chiefs and Wise Ones might know.

We don't even know if anyone but Rand has a clue as to what LTT and the 100 did at Shayol Ghul! We've all read the Strike at Shayol Ghul (probably), but don't know that anyone in our novels really has the same info to any degree.

Birgitte might not remember previous turnings of the Wheel (we don't know how many times she's been reborn in the last two ages). But she has a wealth of info that no one else knows, and asking about it seems pretty dang obvious. That's all.