First of all, why would he? Secondly, she WOULD have woken up, grown ups do that!
You contemplate the possibility that Jeremy made Sheila´s bed before leaving the farm - that makes it very, VERY hard to take anything you say seriously. I can see why I have you on ignore. (Chose to read your posts today - I´m bored...)
Why would Jeremy pick up Sheila to take her into another room ?
How could she have got the gun, massacred the children she was attached to, brutally beaten the father she was very attached to, & killed herself if she was in bed ?
There is no guarantee Sheila would wake up in the 30 seconds it would take to pick her up and take her a few yards. If she did start to wake she would not have a clue what was happening. Giving Jeremy plenty of time to aim.