Why not that spot ?
She had to be taken somewhere as she had to be out of her bedroom. Downstairs was too far, so the only options were with June or the twins.
Or she may have gone to the main bedroom herself.
I cannot see in either scenario the spot being of any importance or any motivating factors behind it.
If Jeremy was the perpetrator I cannot see him giving it any consideration that the location of Sheilas body was of any importance other than being on the premises and the death looking like a convincible suicide.
If Shelia was the perpetrator why would she care either? Schizophrenics don't behave logically she would have believed she was off to heaven ect Maybe she looked out the bedroom window and saw the police? Said her final prayers then finished herself?
There are so many variables and possibilities, Maybe she could have been hiding in one of the bedroom cupboards then Jeremy heard her crying and that's how he found her?
We can only speculate