There are bike trails everywhere here, all throughout the city - and some are along the Mississippi River. I don't know if she got off her bike and went to stand by the river, or if her bike slipped on any icy section of the trail and she fell down into the river. Either is possible. There are a lot of spots along various lakes and the river where it wouldn't take too much of an accident to land you on thin ice and thereby put you at risk of hypothermia. Regardless, I think it's still a good reminder that winter riding has other risks that go beyond the simple task of making sure you're bundled up. Black ice on trails/streets, nearby bodies of water, less people/traffic in the winter and therefore less chance of help should there be an accident, etc.
It has been a reminder of all those things for me, at least. So much time and effort goes into attire and dressing for the cold, that it's been easy to forget about everything else that comes with the change in weather.
"There is nothing more frightening than ignorance in action." -X