When this happened to me, I used the debug menu, dm in console, to get to her. You can activate fly mode and turn on the setting that allows you to move through walls via the debug options that come up when you hit ESC. When you've done that, you can just fly down through the floor to where she is. Sadly, I never found a fix to get her back up to where she should be. No need to use God mode unless you'd prefer its simplicity.
Hell, I tried the trick from A20 to make the POI destructible but it didn't allow THAT instance to be destructible. All new ones found were, but not the problematic one. I mean, if you can make it destructible, you can just open a path to her. Just never figured it out myself.