Oh, she didn't actually head for the floor - she went about 500 feet up, into what looked like a thick mass of branches, tearing a hole through it. Once Ancalagon lowers himself just enough to be safely out of her range but still able to see the moment she steps out, it becomes quite clear that there has been some kind of magic in place to make a very large, open, palatial realm within the upper areas of the forest. For what dragon lacks a castle?