Osea is a holiday park she mentions.
She means she knows Bambers route is populated.
She most probably knows goldhanger and darcy intimately and the sea wall area.
I think De Ath needs to clarify for herself.
Wasn't her caravan at Osea Leisure?
How would she know what was JB's route? Which route? To where?
What makes you think she'd have had intimate knowledge of Goldhanger and D'arcy? It's a lot of sea wall from Osea to Goldhanger, and even more from Goldhanger to D'Arcy, going nowhere, from there, other than Tollesbury Marshes. then having to repeat the journey in the opposite direction.
Clarification would be good.