@GodGinrai
We learned back in chapter 17 that the rings contain a magic stone that is used to detect ghouls.
Blue is for humans and white-yellow is a ghoul.
Might be a difference in translation and the ring is telling us she is a ghoul, or that she has a different colour from normal ghouls because her soul is still intact.
They also used the rings to give people who died and turned into a ghoul a funeral, instead of the bodies.