This is why I said floor----bed-----floor.
That the first shot came when she was sitting on the floor,awkwardly,I assume judging by the angle of the first bullet. Then she got herself onto the bed and when the police were inside the farmhouse,they heard a noise,which would have been Sheila spluttering with the blood running down her throat,so thinking that she could be revived,lifted her on to a flatter surface----the floor,in order to perform CPR.
Did she fire that second shot,or was it an accident by the semi-automatic that was cocked ready,and went off in the process as officers were attempting to make the rifle safe?
On entering,the officers would have seen Sheila on the bed,but they made such a muck of the investigation that it went downhill from then onwards as they tried to cover their mistakes.