This is very interesting. It's possible that the gun had to be held upside down to get the right angle. Couldn't Sheila have done that herself though?
It seems to be overlooked that this woman who's allegedly trying to take her own life, has, allegedly also just killed her parents and her children. I'm imagining mental turmoil. Having PUSHED the trigger once -'coz if the gun is reversed, so too, must the trigger action be- and found herself still alive, I find myself thinking she'd have been all over the place. It's at this point where I COULD believe, providing all the other variables fit, that Jeremy made her shoot herself, but when she misfired, he finished her off with a second shot.