OK - some logical thinking for this one:
Assumptions: Sheila's killed everybody, and now it's time to kill herself (and NO remaining bullets found in the gun after she's found dead)...
- Sheila shoots herself, and it fails.
WHY is there a spare bullet in the gun for her to shoot herself again? (pure luck? did she load with two bullets 'just in case' ?
- Sheila shoots herself, and it fails.
There is NO spare bullet - she now has to go and GET ONE!!!! and come back to the same resting place to shoot herself again?
- Jeremy shoots her, and it fails.
He has to load the gun with another bullet (or there are still bullets remaining), so he shoots her for the second time then makes sure the gun is empty <----- MISTAKE here
For the gun to be empty when found, Sheila either got very lucky and it just happened to have two bullets left, OR she had to get up from the first shot, retrieve and load a new bullet, and then move back to the same place to shoot herself again
I think Jeremy made a mistake leaving the gun empty and didn't consider this strange situation.
Thoughts?