Serana and my character had just climbed out of the cave and into the Forgotten Vale and headed for the first Wayshrine: The Wayshrine of Sight, I believe. My character then jumped down a ledge and proceeded to the Wayshire. I had a sense that Serana wasn’t behind me, but I shrugged it off thinking, she will appear once I enter the Glacial Crevice.

I worked my way though the Forgotten Vale and as I was traversing the white water, working my way toward the Glacial Crevice I was passing by a small ledge on my right, about head high, when a Falmer appeared. As I turned to attack him he fell over dead. I thought, “Serana must be behind me?” And, then thought nothing more of it. After I entered the Glacial Crevice and swam to the other side I turned around to find no Serana. So, I had to open the console and “player.moveto” –since the opposite never seems to work for me. That's when I found Serana stuck on the ledge that I had jumped down from earlier. Since I was using the Dragonbone Bow with Elven arrows I nailed her with an arrow and she fell down the ledge frozen. Then we back-tracked back to the Glacial Crevice.

You have got to love Skyrim for its hysterical moments

Hehe, Skyrim's AI may be improved but it still can have its funny moments. I like your story!