The Question and Answer section for The Mysteries of Udolpho is a great resource to ask questions, find answers, and discuss the novel.
Sorry, this is only a short answer space.
B. The description “as she surveyed through the twilight its desolation” indicates the castle is filling Emily with uneasiness because it looks like a place that breeds solitude and despair.
C. The story is disturbing to Emily because she already feels alone and afraid, and Annette’s story reaffirms Emily’s fears and apprehension about her new life in the desolate castle.