One of the most telling factors for me is the fact that the rifle had little or no blood on it. Had Sheila indeed used the weapon to shoot herself and then wandered about the house before doing so again, there would have been blood all over the rifle. Sheila's hands would have been covered in blood as a result of putting her hands on her neck wounds.

Two things are immediately observed.
1. Sheila did not put her hands on her neck since the blood would have been dispersed more around her neck and face.
2. Sheila did not have any blood on her hands.
3. Had Sheila been walking around, blood would have ran down her neck all the way and then onto her nightdress. Notice how there is no such blood runs in front of her and her nightie is unmarked to the front.
As far as I can see it would have been impossible for Sheila to have done what the defence contend she did do and end up remarkably clean thereafter.
I have absolutely no doubt that girl was murdered.
-------------------------
Police had to substitute bullet PV/20 (the non fatal wound bullet) which was fired by another different gun, downstairs...
Oddly enough, whoever used the rifle to shoot the victims - there should have been more blood upon the rifle, whether Sheila did it, Jeremy did it, or somebody else did it...