Saul believed this woman had the ability to bring Samuel up.
1 Sam 28:8 And Saul disguised himself, and put on other raiment, and he went, and two men with him, and they came to the woman by night: and he said, I pray thee, divine unto me by the familiar spirit, and bring me him up, whom I shall name unto thee.
The woman believed she had this ability.
1 Sam 28:11 Then said the woman, Whom shall I bring up unto thee? And he said, Bring me up Samuel.
The woman said she saw gods come up (ascending) out of the earth (not heaven). When Saul asked her to describe who she saw, she described Samuel and Saul recognized the description she gave.
1 Sam 28:12 And when the woman saw Samuel, she cried with a loud voice: and the woman spake to Saul, saying, Why hast thou deceived me? for thou art Saul.
13 And the king said unto her, Be not afraid: for what sawest thou? And the woman said unto Saul, I saw gods ascending out of the earth.
14 And he said unto her, What form is he of? And she said, An old man cometh up; and he is covered with a mantle. And Saul perceived that it was Samuel, and he stooped with his face to the ground, and bowed himself.
And Samuel himself said he had been brought up.
1 Sam 28:15 And Samuel said to Saul, Why hast thou disquieted me, to bring me up? And Saul answered, I am sore distressed; for the Philistines make war against me, and God is departed from me, and answereth me no more, neither by prophets, nor by dreams: therefore I have called thee, that thou mayest make known unto me what I shall do.
So, you see, it was not just the woman that said Samuel came up, Samuel himself said he came up. And notice that Samuel was upset at Saul for bringing him up. He did not come up willingly.
You say the woman did not have the ability to bring Samuel up? Then explain how he did come up.