SBMFF
They are retired. They were not working within a restricted time frame.
Driving a 5th wheel of that size means that they were not travelling at any speed, probably not even the speed limit.
I do believe they did take a short walk prior, came back and ate a lunch/brunch, then decided to take another leisurely walk.
They are experienced, so I suspect they were well hydrated prior to their walk/hike.
I believe not only are there pictures of her but remnants of their lunch. (plates, glasses,utensils).
What has not been taken into account is that most will stop, rest a few minutes, re-hydrate, perhaps have an energy bar?
I suspect they did once or twice. It would of been at one of these stops were she could of requested her travel mug while she was looking around.
When two individuals have different interests, BT looking for driftwood/rocks, and RT taking pictures, they could of potentially been a distance apart, but still within a comfortable talking/shouting range.
Many have felt she was dehydrated prior to returning and I disagree. I am going on the premise she was in fact quite hydrated.
BT appears fit and could conceivably travell quite a distance. I would not be surprised if she is outside the search area, or the perimeter.