I like Vi and Elspeth the most but I doubt Elspeth would work in a throuple and looking at the guide theres no girl-girl points with her the way there are for other girls at least not yet.
I know it would be too much work for the author to do but the rest of the girls inis/amrit/vi/kana/Serena seem like they could work as a throuple in any combination.
For me Vi has been #1 since the beginning, but I like Elspeth too mostly because I'm intrigued by her.
I think this dev's talent at character writing comes through the most with Elspeth. On the surface, she's empathetic, supportive, and pacifist and she apparently has some of the same demons as MC. But it's also been reinforced so many times that she only shows what she wants to show because she's intensely guarded.
And Zaina being wary of her could also hint that MC subconsciously doesn't trust Elspeth fully and considers her dangerous.
Basically, I'm getting timebomb vibes from her. All of the characters have some shit in their past that they're trying to overcome, but I feel specifically in Elspeth's case it's worse... Like if something sets Elspeth off, people are going to get hurt.