I think the only thing about the lady who found the dog/phone/harness that seems a bit off to me is the circumstances in which she found those things and the timeline. Surely finding those items alone right next to a river, where there is a sign to say that the water is dangerous/deep would at least spur you on to look in the water on raise some concern that there might have been an accident near the water?
The timeline posted by Nicola's friend said that the lady found the dog etc at 9.33 but no further alarm was raised until 10.50 am when her daughter in law went to the bench and recognised Nicola's dog/screen saver on her phone. That's almost an hour and a half. She also tied the dog up with string?? I mean while you are doing that are you not thinking what the heck is going on? I'm assuming police know where she went during that hour and a half period of time, I gather she is elderly so possibility of her doing anything seems slim but there is just something about her account that seems strange. I do believe that she own the caravan park where one of cctv cameras isn't operating.