Recently started a Sisters of Twilight game in Immortal empires by myself after the release of Chaos Dwarfs and had problems getting Ariel. I am Playing on Steam within the recommended specs, game is unmoded and on the latest version.
1: Ariel wasn't given to me upon healing the Witchwood.
I verified Cache of the game ( On Steam ), Restarted and redownloaded and still didn't get her
I continued regardless until I confederated Orion;
2: Orion had Ariel, an Non-player faction had her. I could get her through confederation BUT Ariel Was Missing all her unique items both before and after confederation.
Please make sure when someone is playing Singleplayer that they are the only one to be able to get a unique hero to the faction
and I can only assume that this is also related to her not having her uniques.
Picture before confederation ( the uniques are Orions );