The souls shard were some of those that the engineers had time to scavenge from the corpses of the Nightmare Creatures in the recent battle. That task was important enough that it had to be completed even in the middle of the most terrifying clashes… after all, with every soldier that managed to fully saturate their soul core, the strength of the Song Army grew.
Tamar had long saturated hers, so the share of their cohort was divided three ways between Rain, Fleur, and Ray.