Final answer:
The narrator finds the appearance of Madeline's body striking due to the strong resemblance to her brother and signs of a struggle that suggest her death was not peaceful.
Step-by-step explanation:
The narrator finds Madeline's dead body striking due to the eerie similarities between her appearance and her brother's, as well as the harrowing evidence of a struggle despite her being deceased. There's reference to Madeline's emaciated frame, and something profoundly unsettling about the fact that, although in repose of death, there are signs suggesting that her death was not a peaceful one. The narrator reflects on the striking similitude between brother and sister, and when Madeline reappears, it is with the blood upon her white robes and an expression of having endured a bitter struggle.