Answer:
The doctor tells the family that Elizabeth is close to death. The doctor made a mistake in the medical dosage, and Caroline knows she can do better.
Explanation:
We can argue that Dickinson sees death here as nothing but guide to eternity.
In the poem Death is not sinister nor scary, instead its a courteous and patient gentlemen that is there to guide the narrator even though she had not time for it. He accompany's her until its her time and though then things get bit spooky it is worth it as in the fourth stanza she arrives at her destination which is eternity. She relishes that death is not death, but immortality.
Because all though he knows his sister is dead, he can still hear knocking and scratching sounds coming from her coffin. She's dead, but comes back to life to haunt him causing his madness to grow stronger.
