Doubt it to be honest. I stand by my gut feeling that the river is too slowly flowing in that area to move her downstream quickly enough without either catching on the river bed or washed up on the sides or on the weir. If i fell into water with or without clothes on i would sink.
I agree with your gut, The Truth Is.
IMO, from what I've read the river was mainly shallow and slow moving along where Nicola typically walked the dog, and the riverbank was not that steep that it would cause her to "go in" (even with "slippery stones" leading down from the bench to the water, even with a bouncy dog who "led her on a merry chase" to the water for some unknown reason, none of which has been stated in MSM).
Although there were a few deeper and faster moving spots along the river, including right below the bench (#7 on the angler maps) where her phone and dog were "later discovered" nearby, it doesn't seem likely at all to me that she was right there and during or just after her work meeting on her phone did some kind of header into the drink she couldn't recover from, especially if she was very familiar with the area and was a competent swimmer as has been attested to in MSM by family/friends. There have also been no reports that she or her dog would go into the water in that area on a regular basis, especially in winter, but they may have gone to a shallow beach area in warm weather and maybe the dog went in after a stick or whatever on a usual basis then/there?
And apparently, her dog did nothing in the way of "jumping in after her" if she "fell in" since the dog was dry when observed later on (within 2 hours?). IME, all of the dogs I've ever known of many different breeds in many different situations where they were near or in water continued to have some wetness remain in their coat, undercoat(s), and paws that lasted awhile (several hours), and that wetness not only attracts dirt, sand, mud to stick to their paws that needs to be cleaned off with some resentment at towels and rags and rubbing, but they "stink like wet dog" for a long while (up to days depending).
So to me, it doesn't sound like her dog was able to react to whatever happened to her, if she ended up in the river, with any physical response that would be likely, and was instead "focused on" running back and forth between the bench and gate as reported, where Nicola probably did go askance, IMO.