Excellent analysis, Roo, Rose, and Cameron. Guilt. Mother. Belonging. All legitimate in my eyes. Here’s my take on the story’s key themes:
I suspect that every waking hour, whether conscious or not, Erin regretted her decisions in the past. It is inevitable she has to face down those dynamics. Hence, the tragic case from her past emerging again in the present: Call To Adventure.
Redemption due to her complicity in the past tragedy. It’s almost inevitable for stories which start out with a Protagonist having screwed up in the past to seek out a path toward redemption.