Who's to say that Sheila didn't freeze?
Who's to say that Sheila hadn't just woken up and wandered into the bedroom moments before JB returns upstairs, almost paralyzed by fear, she stumbles over and is already on the floor when he approaches?
There are all sorts of permutations.
The 'freeze' theory has been discussed on here and can be dismissed in five seconds. Even if she did 'freeze', she must still move or be moved, so you still have to explain a great deal and 'freezing' doesn't explain any of it.
Now you suggest she may have stumbled over, which goes against what you said earlier when you tried to suggest that just having a rifle was enough for Jeremy.
It appears that, like everybody else, you don't have a single clue how it happened. You are just guessing. But you maintain Jeremy did it. You are entitled to do so, of course.