I live about 3 miles away now but I did used to live in the village, about 8 years ago.
Here's a map of where she was.
The cross is where she accessed the river towpath, the circle is the bench and I've underlined the house on the other side of the river.
As you can see, to get to that house, she'd have to go totally back where she came. You can't cross the river to it either because there is a huge wall that you cannot climb.
As to what what happened, I'm stumped. My first guess is she went in the river, but there are no signs on the bank of her going in and it was also shallow at that time.
It's also possible she was taken to the caravan park which is just above where the bench is on that picture, but I can't understand why the dog wouldn't follow if that's where she went.