Just to be really clear on all the points about the dog - even if Willow saw Nicola enter the water, Nicola would likely have only been visible for a matter of seconds before being submerged.
If you haven’t read the post about cold water drowning, it’s very informative about how quickly and silently it happens. A dog would not understand, and it certainly wouldn’t think its owner was playing - there would be no thrashing about like in the movies.
Yes, spaniels generally love water, but they will often only jump in a freezing river if they’re following a tennis ball.
Yes, spaniels (and dogs in general) are fiercely loyal pets, but they are also animals who don’t understand that human disappearing in river = human drowning. They just think it’s like when you walk out the front door, and you’ll be back a bit later. Except they’re outside in the cold.
Yes, some dogs bark if left outside a shop. But some don’t. Spaniels aren’t really vocal dogs in general.
The fact the dog was dry only means the dog didn’t go in the river.