To my way of thinking,Sheila had handled the silencer by trying to fix it to the rifle thinking it may dull the sound of firing and because of her erratic temperament,scratched the silencer,as DB had pointed out the mark on it,but she wouldn't have put it back in the cupboard. Was that fingerprinted ??
This is not to say that Sheila used the silencer,but it wouldn't have been her blood on it at this point,nor at any point,so it's a mystery as to how the blood got there if allegedly it was Sheila's. How would Sheila's blood have got on the silencer ? Always supposing it was hers ?