I’ve posted about this earlier so my apologies, you’re right, it’s not deep, I’ve been in it right up to the top of my waders in conditions similar to this in summer, if anything the river is lower now than at points during the warmer months. It’s not overly fast either. That being said as children we were always warned that you can drown in water only a few inches deep. I’m not a scientist so take this with a pinch of salt, but I don’t think the river is deep enough for a body to float very far before becoming visible from the bank.
Obviously being close to a river causes your % chance of ending up in a river to go way up. The % chance that someone would fall in, not be able to get out, drown, become snagged in a hole permanently out of view and not be found 3 days later in that particular river is pretty much 0% IMO. I think people might be visualising big, deep rivers like the Severn, Ouse, Thames etc.
I also saw a post here stating that the dog wasn’t wet either. That means one of two possible causes for her ending up in the river is ruled out. Leaving only that she fell in without the involvement of the dog. What are the chances?