Forgive the nitpicking here, but this one doesn't really count. Kitiara's death was part of Dragonlance's Legends trilogy of novels, and while Caradoc (Soth's senechal) said that he retrieved her soul from Takhisis's realm as Soth ordered him to in James Lowder's novel
Knight of the Black Rose, he refused to turn it over, and we subsequently see her spirit during the Summer of Chaos on Krynn, working for Takhisis.
Insofar as Sithicus goes, while the original backstory for Soth being a darklord says that he followed her voice through the mists, that was stated to be a false rumor at the end of the aforementioned novel. Likewise, while the description for Sithicus in the 2E campaign setting books says that her spirit haunts the realm to torment Soth,
When Black Roses Bloom (affiliate link) confirmed that this wasn't the real Kitiara, but was instead a duplicate created to torment Soth.