Abby Primo's response to Dacus

I think that Usher knew that his sister was alive.  I think he knew because he did not bury her in the ground.  I know he did not want her body to get stolen, but I also think he did not want to bury his sister alive--out of sympathy or insanity I am not sure.  Another reason I think he buried his sister alive was out of insanity.  He gave me the vibe that he was insane throughout this story.  I just think he was not in his right mind and decided she was dead and put her in a coffin.