Just adding my two cents.
I've been dipping in and out of these threads (so sorry if I'm repeating things already said), her disappearance has been on my mind. I guess it's because of the the short time-frame she disappeared in. I think she fell in the water, whether it be an accident, crime, or suicide (I believe accident).
I do think people underestimate how easy it is to drown. I grew up near the sea, and an estuary. I love water, swimming and the beauty of it.
But I also know the dangers. It was drilled into me as a child.
In my late teens I volunteered as a beach lifeguard, in my mid 20s I went on to join the RNLI for a few years. I'm only writing all of this to tell you that I know how treacherous wild bodies of water can be, also drowning isn't like in the movies or tv shows. It's mostly silent. An arm in the air, a head bobbing above and then going under the water.
The fact the water would be ice cold, and that she was wearing winter clothes also adds to her inability to save herself, and even if someone had seen her, they also probably wouldn't have been able to save her.
Her dog, is not an issue in the case for me, dogs are not like Lassie, they don't always alert others to trouble, or heroically try to save their owners (even if they love them) they are animals, and will act in line to their nature.