This is a very good well thought out theory, and sold as such, nice change on this forum.
It is believable. I don't have a theory, I enjoy reading and listening to realistic ones. JT-something about this I feel uneasy about. why would she change her time to sit in with Gerrys story?
With the caveat it is a theory and quite possibly wrong, my view is ...
The JT sighting is not essential: MBM could have been alone and taken the tracker dog trail.
If, however, she was walked away by an unknown third party, the tracker dog evidence would appear to be the same. At the end of the tracker dog trail it is possible the third party decided to carry her.
The general direction of the trail is towards the east. The tracker dog trail is circuitous, but there are simple reasons why it may have worked out like that. The thrust of the direction is toward the east, which is the direction reported by JT. There is, therefore, a coincidence: the possible sighting of a third party carrying a bare-footed child in the correct direction.
IMO the reported timing of the JT sighting does not work well, but perhaps she was simply mistaken as to when she made the sighting. There is common agreement she left to 'relieve' ROB, and this is probably established fact, and perhaps this is when the sighting occurred.
There are two potential anomalies in the statements with respect to the sighting: (1) GMcC reports the JT as being 50m from the individual, which would place JT at the entrance, and (2) JT reports:
4078 “And was that, is there another pavement there, on the junction?”
Reply “No, they were on, there’s a junction, this is sort of the road and they were walking along the side of the pavement, then I would then walk along”.
4078 “So they were on the same side that you were about to walk along?”
Reply “Yeah”.
I'm not clear how to interpret those comment.
Anyway the JT sighting is not essential to the theory, but it is possible that it would fit if the timings were different.
The question why JT reported the sighting at a different time could be down to fallibility of memory, and the possible accidental contamination of memories because of the discussions that took place before the police interviews. All the parties that night are likely to have been shocked about events, and, perhaps, misremembered the times and frequency of the checks that were made.
All IMO, and not an attempt to displace any other theory.