I really have a feeling that Avanti can "steal" other's appearances like a doppleganger. While they're busy outside the walls, disguises into one of them and go back inside and attack the loved one of the one she stole the appearance from ( knowing who it is by "magic" or whatever, it's a spirit, she can know ).
Ranach said the blood would come from the inside, and wanted the tribe dogs to find the shrine so he obviously placed it with some tactical/warfare planning advantages there.