Why was Turtle startled when she looked in the coffin in "The Westing House"?

Turtle had entered the mysterious and foreboding Westing house a few nights earlier.  It had been Halloween, and she went into the house on a dare.  Dressed as a witch, Turtle had her pockets full of miscellaneous items, among them "her mother's silver cross to ward off vampires".  Lured by "a throbbing whisper", Turtle had ventured to the second floor of the house, and had discovered a corpse "tucked in a four-poster bed" (Chapter 4).

When Turtle returns to the Westing house a few days later for the reading of the will, she notices  "an open coffin draped in bunting rest(ing) on a raised platform at the far corner of the room".  She is startled when she looks into the coffin - "in it lay the dead man, looking exactly as she had found him, except now he (is) dressed in the costume of Uncle Sam...including the tall hat...(and) between the waxy hands, folded across his chest, lay her mother's silver cross" (Chapter 5).