Statesboro, GA, USA
First: she had a familiar spirit, as Saul was told. Familiar spirits, then as now, were possibly demons, who pretended to be a person brought up from the dead.
Possibilities surely may be considered in biblical interpretation, but only after certainties have been established. To posit possibilities above what is more concrete and obvious, leads to interpretive error.
Here are the certainties about this passage that I see:
1) The author of 1 Samuel writes as if Samuel were really himself. So not only do the characters of the story seem convinced that Samuel is really himself ... the very author does to! There is no textual evidence that he (the writer) doubts the reality of who Samuel is. Consider the following verses, which never state things like "the spirit who pretended to be Saul said" ... or "that which was percieved as Saul". Not only do these verses not say such things, they don't even hint at a ventriloquist act:
"When the woman saw Samuel, she cried out at the top of her voice and said to Saul 'Why have you decieved me? You are Saul!" (1 Samuel 28:12)
"... Then Saul knew it was Samuel, and he bowed down and prostrated his face to the ground." (28:14)
"Samuel said to Saul, 'Why have you disturbed me by bringing me up?' (28:15)
"Samuel said, 'Why do you consult me now that the LORD has turned away from you and become your enemy?" (28:16)
"Immediately Saul fell full length on the ground, filled with fear because of Samuel's words" (28:20)
2) Samuel is true to his manner of dress, his character, and his vocation.
- Samuel's dress /garb: "'What does he look like?' he asked. 'An old man wearing a robe is coming up' she said (1 Samuel 28:14)
- Samuel's knowledge of Saul's history: "Why do you consult me, now that the LORD has turned away from you and become your enemy?" (28:16)
- Samuel's speech on behalf of the LORD, as a prophet: "The LORD has done what he pridicted through me. The LORD has torn the kingdom out of your hands and given it to one of your neighbors- to David. Becuase you did not obey the LORD or carry out his fierce wrath against the Amalekites, the LORD has done this to you today. The LORD will hand over both Israel and you to the Philistines, and tommorow you and your sons will be with me. The LORD will also hand over the army of Israel to the Philistines." (28:17-19)
3) Everything Samuel said came true:
"When the people of Jabesh Gilead heard of what the Philistines had done to Saul, all their valiant men journeyed through the night to Beth Shan. They took down the bodies of Saul and his sons from the wall of Beth Shan and went to Jabesh, where they burned them ..."(1 Samuel 31:12-13)
So to summarize, despite the difficulties that Samuel actually being summoned from dead would cause, this is the most natural rendering of the text. And it seems to me that you run into far more difficulties interpreting the spirit of Samuel as an imposter or a vision.
Those difficulties would be:
1) The biblical author of 1 Samuel would have to be either deceived by this spirit himself, or a deceiver of those he wrote to. Either of which throws enormous problems up against the doctrine of divinely inspired scripture. Would God allow such a misguided deception exist in the author?! Or, worse, would he allow such a deception to exist in his written word, to whoever may read? Because the text clearly reads (with not even a hint otherwise) as if the spirit spoken of were actually Samuel himself, both with the Characters and narrator himself.
2) A demon, or imposter spirit, would be giving the utterance the LORD's word, and direct accurate prophecy, rebuking unrighteousness, and even exalting David (a type of Christ) in his speech to Saul.
3) The most obvious reading/ understanding would have to be rejected, for a much more elaborate, contrived, interpretation ... the kinds of interpretation that come often from a strong desire to salvage some other point of belief. I'm not saying this is done with bad motives, or even consciously. (I'm sure I've done it too). But the principle of Occam's razor, actually applies to scriptural interpretation too.
I don't have time to get into the other passage about the mount of transfiguration yet ... but soon maybe.