They are, and they've come much closer than anyone else. They actually destroyed Xykon at one, and when he had an entire army at his back at the other, they delayed them long enough (including his various elites) to a point where if it weren't for Miko he and Redcloak actually would have lost. Even basic recon like O-Chul's record of Xykon's spells known would be extremely useful intel for Serini to have, and it's info she could reasonably expect them to be tracking.
Refusing to even speak to the folks who've fought him and survived, much less fighting him and almost winning, is foolish. The only justification for that I've seen, her wanting to keep the element of surprise over them, is flimsy - she clearly has resources they would never even think to ask about, and an Epic Rogue could lie her ass off in a sending to V if needed besides.
She may not know the growth bit, but she definitely knows they know the stakes, because Lien specifically told her they do. (I mean, she might think the paladin is lying to her face about that maybe?)