Well I wasn't paying much attention to the flow of the story when I was translating but now that I think about it, I think the koReimu realizes the Deibuness of her mother but just reluctantly accepts it and sings the song. At the end, I assume the other yukkuris hated the koReimu for singing and not helping and killed her.
I'm not sure if it's the mother reimu talking or a narrator. I wasn't sure about the perspective of the story so i just translated it from the yukkuri's perspectives.