Something like the following, probably:
“I pushed you in the desert because I needed to see it… I needed you to see it… who you are. The dark side is in your nature, Rey…”
“You’re lying.”
“I’d never lie to you… your parents were no one. Junk traders expecting a child they never planned for.”
“Don’t!”
“Your father had no part in your conception.”
“I don’t want this!”
“…just like Vader.”
“No!”
“You see it, too, don’t you? The throne.”
(Rey sees a flash of the vision of herself on the Sith throne)
“Your family feared you. Just like mine did for me.”
“Stop talking.”
“Rey… our parents abandoned us to murderers.”
(Cutaway to heroes capture)
“Your parents were always drunk, especially so when they sold you. Palpatine’s followers captured them. He was looking for you, but they couldn’t even remember what happened to you. They died to ensure you never saw a second chance at love.”
(SOME SORT OF VISUAL HERE)
“No!”
(The mask of Vader falls to the ground)
“So that’s where you are.”
“Before you chose the Jedi, Palpatine wanted you. I’ll come tell you why.”
—
“Why did the Emperor come for me?”
"Because he manipulated the Force itself into creating life. My grandfather. Then, perfected in darkness with you. You’re his chosen heir… a rightful Palpatine.”
"The Emperor only wants us to fight each other so his strongest heir may take the throne. But he’s unaware that we’re a dyad in the Force, Rey… a bond, not of blood, but shared power. We’ll kill him, and finish what Vader started, together…”