Elderscrolls.wikia only lists followers getting stuck in there as a PC and PS3 issue but as of dawnguard at least, this seems to effect the PC as well.

A simple workaround is dismissing her, although I dont know where she returns to at this point.

If this happened to someone at a point where they couldnt dismiss her, perhaps just after recuing her, it would be rather game breaking.

EDIT: Nope. Dismissing her didnt work. It causes her to turn invisible (oddly enough) although she remains in the came and you cant interact with her.

ignore this