Although she was menstrating neither was there a tampon inserted..
An empty tampon package was found to be present in a different downsnstairs room..
downd
Why wasn't Sheila wearing any knickers beneath her nighty at the time of her death?
A) She'd run out of clean knickers. She'd only taken enough for the length of her stay and was going home imminently.
B) She was disturbed -mid 'operations' ie, tampon box in hand- by the killer.