Sadly her husband is still foremost in my mind as the reason she's missing....
HOWEVER: if she liked to meander about, and it sounds like this was a casual outing, a short walk, take some pics - she's walking @ with a beer in her hand - I could see her finding something of interest: a plant, a rock, simply a desire to walk out on the rocks. She could have been bitten by a snake or scorpion, or fell & hit her head & become unconscious.
Her husband could have passed by where she was laying, unseen.
She could have awoken & been seriously disoriented - head injury, possible snake bite, any other kind of medical situation on top of this - stroke, heart attack.....
Point being she may have then wandered very very far from where they were initially & went in the entirely wrong direction.
Now, I would think, though that Search/Rescue, dogs, etc. would have been able to pick up a lead.....?