Not having an annotated text, I read this and wondered wy she would wear black ribbons under the circumstances. My answer to that is that the Elliot pride would indeed require that the Elliots wear black ribbons for the heir's wife, even if they only learned of her death in the papers or by word of mouth. I would have thought that they all would be wearing black ribbons, and Elizabeth's are the only ones mentioned because this passage is addressing her history with Mr. Eliot.