This is Chapter 13 in Volume 3 of A Place Further Than the Universe
The expedition team is arranging a journey inland to where Shirase’s mother disappeared. This brings back memories for Shirase, of hearing the news about it. She isn’t sure that she wants to go. The other high-school girls discuss it with her. Shirase says that she feels normal, and explains, “Once I go there, there won’t be anything left. That’ll be the end. If I go there and nothing changes, then I’ll keep on feeling this way for the rest of my life.”
Shirase discusses it with Gin Todo, then counts out the million yen as she thinks. As the snowcats make ready to head out, Shirase joins them.
This chapter is based on Episode 12 of the anime.