Imagine, for one moment, the batch of crime scene bullets / bullet cases and control ammunition handled at the scene by the police, yet not one of them, or even the experts at the lab' got lead deposit on their fingers - with this in mind, why would Sheila necessarily have lead deposit on her hands / fingers, if none of the prosecutions experts who handled the same had none, or reported none on their fingers, or hands?
Did Sheila have special hands / fingers upon which lead deposit might be detectable?