Don't forget a sheet from the bedroom was missing too. That's really the only suspicious thing, and Sandra's daughter noted it missing when she checked the house.
That's also the same day when she found some 'evidence' under a piece of furniture/wardrobe/cupboard. We have never found out what that is.
Of course we also have the fact that Sandra's daughter was the first person in the house after the alleged incident.
<modsnip - not victim friendly>
I'm ruling out suicide. It doesn't fit, IMO. She always lived a life of being look-after, and had no previous attempts or even signs of depression. She was taken care of. She liked looking after her grandchildren. I know some people exhibit no signs, but if she was depressed and suicidal, she could've killed herself in her house. Also, no body or remains have been found in walking distance locally.
An accident while out walking is possible, but unlikely..... there are a few local pond and lakes, but again, no body or remains found, and why would she suddenly go out walking in the evening when it's dark after expecting a call from friend about her visiting? She wasn't a known walker in the evening, or at all.
LE seems to be no wiser as to what actually happened than we do and I think sadly, this may remain a cold case for many years.