I really don't like thinking about this particular part of events, but I can understand the debate and it's undoubtedly key to working out what actually happened. I'll try to be brief here, and then I'm not touching it again.
The stretch of the river after the park is indeed largely industrial until it reaches the city centre. Lots of business premises open directly onto the river between Clough Road and Wincolmlee, but the area is a ghost town over the weekend. There's also a lot of dereliction and disuse. There isn't much in the way of public access to the riverside. Check streetview and you'll get a feel for it.
As well as buoyancy and variables along those lines, I think the reason that nobody saw her is simply because nobody saw her. If that sounds obtuse, I had a crack at explaining what I mean with an amateurish Schrodinger analogy yesterday. The river is extremely brown, and if nobody was around to see, then nobody saw.
In all likelihood it didn't take 7 weeks to reach the estuary. Travel was probably further and faster than most of us are reckoning. Once in the Humber, it's good fortune she was found.