april maybe AE thought Sheila was sleeping in the double bed where her body lay before being put on the floor as she knew Ralph and June usually slept in the twin beds and as her body was found on the double bed she assumed that Sheila was using that bed if I am waffling ignore me.
I have to say that's a good thought Susan, it is a possibility, especially as Nevill was having trouble with his back and maybe was more comfortable in his own bed, so they spread out into the other room as well.
It reinforced the fact she told Julie that Sheila was found on the bed in the main bedroom.
Ralph must have usually slept in there because there was no surprise from AE that his slippers were by that particular bed.