Imo alot of Sivir's lore was left hanging in mid story after the Shurima event. Heck, I don't even think Riot ever said it outright if Sivir even knows that she's the decendant of Azir. Sure, its implied with her lore that she kinda knows but when did she have the chance to find out? I mean, Azir himself didn't really know, so how did Sivir find out? Even if Azir somehow knew, Sivir only knows him through his Chicken form. Did a giant chicken wake Sivir up and tell her in a masked heavily breathing voice, "Sivir, I am your great grand father."?? (Sorry, the Star wars reference oppertunity was too good to pass up) I'd imagine that Sivir would question her sanity even if that did happen.
But that's not all, how did Azir's return impact Sivir? It said in her lore that whatever she found in the tomb changed her life. Howso? I can't imagine Sivir being able to do anything with knowing that she's Azir's decendant. Yeah she's theoretically royalty, but how does that change your life if you're the royalty of city ruins? And why would that matter to a mercenary? I simply can't see this being useful/impactful unless it's a requirement to ascend? (Ascended Sivir skin plis riot)
And why / how did Sivir become friends with Nasus??
How does an oversized hound guardian get to know and be friends with a mercenary?
1) How did Siv/Azir find out their blood ties with each other? Even if Azir had powers to tell, Sivir would have to trust a giant bird telling her that she's his decendant.
2) How does knowing Sivir's heritage "change Sivir's life dramatically"? (Paraphrasing her lore) What'd she do with that knowledge?
3) How does Nasus get to know, meet, and befriend Sivir? One being a mercenary and the other being (I think) a guardian hound? (Says the two are friends on Siv's lore page)