I doubt very much if any statement made by JT, or any other witness for that matter, is ever analysed in splendid isolation.
The norm when the broader picture is viewed is I believe for investigators is to seek corroboration.
For example – the question is not as you seem to think – did GM and JW deep in conversation see JT walking past on her way to check her children. The question is, did JT see GM and JW.
We know that JT left the tapas table and we know that she confirms the meeting of GM and JW. She saw the pair of them.
What we don’t know is exactly where CB was at that moment in time. As the prime suspect in a murder CB’s whereabouts surely take primacy over a witness statement. Which despite being checked and double checked for over sixteen years and one would have thought having had its share of myth and innuendo exhausted over that period.
Alas! It seems that is not the case. But further slurring a witness who was traumatised by the belief that she saw MM being abducted is not really of the same importance as finding out where the prime suspect was. My opinion
Well that's the point - it isn't collaborated and we know they all discussed their accounts. It just really isn't possible to exactly reconcile her statement with Trottman either - yet somehow the Met came to a broad conclusion
There isn't really any reason to prefer the evidence of JT over GM+JW (2 people).
I think @Janosch is correct - she came by later after they were gone.