That sounds like you're saying he did it on purpose, but either way, once it was botched, he couldn't turn back could he? It was done and he's have to proceed. The best that he could do was to make them believe he was elsewhere - hence the phone call.
What I was trying to say was - that if he had botched her suicide by failing to kill her outright - then that's a MASSIVE blunder in his plans. Quite why he would think she would immediately die from one shot is beyond me anyway - as he had just pumped multiple shots in to all the other victims! So where is his reasoning going - by thinking he could finish off Sheila as the last victim with just one shot? Again - it doesn't add-up.
I guess they could have said it happened while they tried to get the gun off her, but that's not for me to explain given that I don't think the police did shoot her - Jeremy did.
Aah but this is getting to the crux of the matter though. You have consistently argued that hypothetically, the police would have no need to explain or hide the fact that they shot Sheila in the course of their duty.
However it's not that simple is it? If it's the murder weapon that actually killed her - it's not that simple to explain. Yes - they could say struggle etc. Nevertheless - those in the know about tactical firearms operations and police tactics might raise an eyebrow or two.