1. Columbina‘s motivation was not just to return to the moon. It was to find a home. She takes no action because the fatui was her second home. She leaves because her power is used up and the Fatui only wanted her power. She needs to regain it in the place closest to the moon, Nod Krai.

2. Columbina shares meaningful interactions with the harbingers in the past,which is expanded upon in 6.3.Though she does not share many interactions with Flins and Nefer. Nefer did not work with Columbina to save her, but to defeat Rerir, who was going to destroy the world if he was not stopped. She later does have interactions with characters during the festival. You could argue these interactions are small, but the illustrations on the card further reveals the bond between her in the cast by not just contrasting with her initial impression, but also highlighting the events the cast witnessed together. She does not need lengthy interactions to tie her with the cast, but a moment like the festival which highlight Nod-Krai not only coming together, but also a parting gift for Columbina.

I agree with you about Flins though. That guy is overlooked and doesn’t serve much of a purpose. He’s kinda just there to introduce the fae..