As I said, Sheila didn't hate her dad so mayhave been reluctant to kill him at first.
The silencer most certainly was not on the rifle when Nevill was prodded in the arm!
Anyway. you are the one with the enormous IQ, General, you tell me the reason why Nevill was killed last?
Here we go again, you sausage, you answer the question so I can rip it to bits.
...and the first bit - 'may have been reluctant to kill him'? This might make sense to you, but are you now suggesting that she somehow managed to bludgeon him senseless and popped upstairs and killed everyone else but him? Then when he regained his senses was quite annoyed at being beaten half to death and wanted to have a stern word with Sheila, so dragged himself upstairs?
Then, of course, she committed suicide with that commonly used method of shooting oneself in the head twice, uisng a long-barrelled firearm; a method used in a vanishingly small number of successful suicides. And don't get me going on the almost certain loss of motor fiunction following the first shot.