Did she? You do know that stomach contents is a very bad indicator for TOD?
It shouldn't be,as under normal circumstances it takes 2/3 hours to reach the small intestine through the digestion process.
Okay,if she'd have eaten at midnight,and died at midnight,then obviously the food would remain where it was,undigested,but the girl would have been a darker colour,after the pallor of her complexion that we've all seen,and because LM had only started ( visible in her legs,underneath ) which comes on about half an hour after death and up to 2 or three hours for it to become visible.
So presumably the tragedy happened after midnight,so Sheila would have had to have been killed immediately after eating,whatever time that was. So count back 3 hours at the most for LM to be visible,from the time she was found.