Zorro, take one step back to the "Everyone Who Feels Disappointed..." thread to see how much company you have! I don't know if it's even possible to top the viciousness of that last scene. Mijin came across as having gone from merely annoying and repulsive to being a flat-out psycopath. This should never have been permitted to get as far as being broadcast. They should have either re-shot that scene -- and shot the writer -- or thrown the entire project in the Han River.
It just occurred to me: Perhaps Mijin was channeling the old lady? There's just no explanation for that final scene.