I'm have trouble getting invested in Cait because it feels like she left the temple and chased after her sister cause 'she had to for the story'. Was her goal simply to bring her sister back to the temple to live with her despite it clearly being a life Calla despised or did Calla actually leaving make Cait think "Oh shit, maybe I'm missing out on something more in life"?
You
have done all of Cait's conversations, right? Because she answers this right at the start of the game if you ask her about her family. Calla wanted adventure and to see new horizons, Cait was happy at the Temple but wanted to be with her father and Calla
more so after agonizing over the decision for a while she left to join them, but not before getting her brand because she hadn't made up her mind by that point. The three of them were traveling together for a year or two before the start of the game so there was absolutely no 'I must bring Calla back to the Temple' about it, Cait wanted to see the world too and she wanted to do it with them. She mentions that her mother even encouraged her in this.
There's followup to this once you complete Cat Call and can talk to her, to Barney and to Sally. While there's plenty of room for further writing, two branching paths for her and a few teases to future story content for her, Cait's motivations for being in the Marches in the first place are pretty established at this point.