Quote Originally Posted by Buffalobiian
Considering they're elves...
The priest only mentioned that Riannon's family line (including her brother Arthur) is descended from elves. They are a lineage that comes from survivors of the long-extinct Age of Elves. The opening sequence showed that a force (presumably Arwan) destroyed each Age, Golden, Silver, Bronze, Giants, Elves, leaving us now in the Iron Age. She and Arthur are not exactly elves, but they are related to that lost civilization. The others in their village are 100% human.

@Kraco:

They never explicitly stated it, but it seemed like Riannon was left alone in the village because someone, probably her since they called her an Oracle, predicted that the priest would be coming. They sent all the women (additional potential sacrifices) out of the village along with the children and elders, while the men went off to hunt, getting them out of the way as well. She was ensuring that no one else could be harmed. She kept the arrowhead with her to kill herself and foil their plan, but sadly the children were not informed and ruined the plan for her.