As fun as all of these ideas sound, surely the most likely thing to have happened was that she was sat on the bench, engrossed in her phone/ meeting, and chose to have a closer look at the river, falling in for any number of reasons.
The lead, phone and dry dog explains so much, and just make other possibilities so much less likely
If someone had come by, I doubt she would have left her phone, it's the first thing people reach for. However, if she was looking for her dog which had gone out of sight, I can see why she would leave it on the bench on the call while she checks the river, or even just having a look while the meeting didn't concern her.
If she had left on foot the dog would be difficult to stop from following, not to mention the cctv coverage appears to be strong, it's clearly a fairly busy location, her stuff was fairly far away from any vehicles, someone else being involved just doesn't seem particularly plausible, especially without evidence.
It's proven that the river has the power to move a body at least 7 miles over that exact stretch as shown by the previous case.
I really don't see much evidence against those theories, she could fall in with absolutely no trace of falling in, the lack of evidence of that isn't a big red flag to me. She could fall in without the dog realising, or the dog could choose not to enter the water.
I think the police are correct, given the limited evidence, to be putting the most resources into the theory that she fell in to the river, with no others involved, I'm sure they're also putting time into other theories, but some of the ideas on here are so implausible. It's nice to play out the ideas, but accusing witnesses when it's just so improbable seems a bit far, the police will have treated everyone involved with suspicion until they're able to verify their alibi's
It seems like some on here see any evidence and before thinking it through jump to a conclusion
They've jumped on the OH, over absolutely anything, the house has CCTV and he was working, there's no way the police haven't thoroughly checked his alibi.
The person who tied up the dog, the rope has been questioned, but again, it could have just been laying around, it's not in and of itself an indication of something bad, again, the police can and probably have checked out the appointment - we will never hear people's alibi's, its an invasion of privacy to share what people are doing
The similar looking family friend, her boss, the google maps guy, the list goes on, but all the theories are so easy to check out and the police will have already looked into all of these people, because they probably take about 10 minutes each to rule out
The fact that she hasn't been found doesn't mean someone else was involved, the bench is meter's from a weir, after which the river is intertidal, making tracking a body extremely difficult, the one from years back took months to appear, the sad truth is that the most likely scenario is she will be found at a later date possibly after the search is called off, and we'll always have questions about how it happened
That's not to say there isn't foul play, just that, it's unlikely and there's nothing to yet lead anyone to believe anyone else was involved