The missing sheet is the bit that bothers me.
But then again, Sandra's daughter stated this, so who knows what to believe.
It must have been actually missing off the bed for her to have noticed this.
We still have no context for this, assuming it was off the bed. Was the bed made when this was observed? Did Sandra normally make her bed every day? Or did she leave it unmade? Was she fastidious about making sure top and bottom sheets were both always on the bed?
The boys were there right until Sandra left for the mechanics. Did they take naps in Sandra's bed? If a child had an accident, I do not believe Sandra had laundry in her house. What would she have done with soiled linens? Laundry bag? Basket? Were these checked?
Personally, I can't give much consideration to such a small fragment of information without such context. And I come back again to the conclusion of law enforcement that there were no signs of struggle in the house.