The fields are quite small - I recommend looking at google earth. Someone has uploaded some ‘street view’ shots all around them.
I am very confused why we have so little information about the two sightings (lower field and upper field) especially regarding the witness movements.
If you are in the upper field, for example, you can easily see anyone else also in the upper field. So, depending on which way the witness was walking and where NB was they would maybe have seen her enter the field and walk about. Where was she? How long was she in the upper field? Which way was she headed? (Towards the beach as seemed normal on her route, yet Willow was dry so they didn’t make it there. Why not?) Which was was the witness walking and how long did they see NB for?
For instance, the spot marked on the map as Sighting 3. Was NB heading towards the beach area? If so, assuming the witness was heading towards the caravan park, they’d have seen NB come into the upper field and walk across and down before passing her. Did they interact?
Or, alternatively, where they headed down towards the river from the caravan park, in which case they’d have been watching NB for some minutes wander about the upper field before meeting her heading up the path?
Similarly for the lower field sighting. Where was NB? Where was the witness? How long did they see NB walk Willow for?
What time did they first see NB and for how long?
I think, if there is some other explanation for her disappearance, that these witnesses and sightings are crucial and I can’t believe so little concrete is in the public domain.