With regard to the possibility of a 3rd party being involved, there's been a fair bit of discussion about how such a person could possibly know that her camera and audio was on mute, and considering that they would not know that, wouldn't the fact that she was on a call/ in a meeting, be a major deterrent for any potential abductor/attacker??
I tried to imagine the scenario as we believe it to have been, from the perspective of someone watching from a relative distance, as a potential stalker or abductor may well do.
You see NB, perhaps stood near or sat at the bench , phone either in hand or layed next to her on the bench. A voice or voices are audibly coming from the phone but you are not close enough to hear exactly what is being said.
You see the dog run back and forth, returning to its owner, maybe waiting for a stick or ball to be thrown again, you hear NB talk out loud to the dog whilst the voice from the phone continues uninterrupted.
At this point I think you would make an assumption, maybe not even very consciously, that the voice coming from the phone, can not hear you back. Maybe you just assume that it's YouTube video or an audiobook playing or something of that nature. But I'm fairly sure I would be able to sense that it was not a two way interaction.
That said, I have felt fairly confident up until now, that for whatever reason, the most likely place she could have gone was into the river. But as time is dragging on I am starting to question whether something outside of what is most likely or feasible has possibly occured.
Whatever may have happened and whatever the outcome, I only hope that she is found so that her family can at least know, even if nothing else. The anguish of being in this state of limbo is just too cruel and unusual to imagine.