I think there might be two lines that lead to Cecilia winning over Kiana.
One (more likely), she's able to deduce who/what killed Reva. Giving that knowledge to Kiana could lead to gaining her allegiance, or at minimum her ongoing gratitude, as Reva was the only one other than Milfina who could actually go toe-to-toe with Kiana, something she holds as the highest importance in her quest to "have fun" in contests of strength. If Kiana finds out who stole her homoerotic rival-slash-love interest, I could see Kiana deciding that Cecilia is an alright person, and might cooperate with her.
The other, is if Kiana has a surprise sweet tooth and the otherworldly pastries and baked goods Cecilia can make end up making Kiana fall head over heels. I don't know if I'd appreciate that sort of outcome because it feels a bit non sequitur-ish, but we saw the pastries win over Reva, so there's a through-line there for strong individuals liking tasty baked goods (however infinitesimally flimsy and reaching it may be). We also had Cecilia bake stuff for Milfina already, so I'm even less inclined to think that'll circle back around once more with one of the Four Generals, but, "every thread is valid until it's not".
Otherwise...interesting that Reva was not killed by Kiana, just on its own face. Learning more and more about each of the Four Demons under Milfina is just fun narrative development on its own, but it does open up the continued strangeness behind what all is happening.
The hero of the goddess not dying to one of the Four, only for that proclamation to be made across the realms of humanity, underscores how suspect all of the information humanity & Cecilia (and thus us the readers) have regarding the invasion of the Demon King. We're still very much in the first portion of this story, so I expect a lot more questions before we get any real, definitive answers, though...so I kinda expect that alongside that, we'll be getting at least a few bouts of misdirection to keep things interesting.
Hopefully it all ties together and doesn't feel like things are pulled out of nowhere to justify weird reveals, but I'm enjoying this mounting sequence of oddities that betray the fact that really nothing is as it seemed.
Thanks for the TL.