Though generally not a fan of Jennifer Connelly’s one-note performance as Sarah in Labyrinth [where that one note = HUH???], I do love the way she delivers that line. She starts off reciting the little climactic speech from the play that she was struggling with in the beginning.
As she begins, you can see her speaking pro forma, mouthing the words because that’s the function of the Protagonist during a Showdown with the Antagonist. Staring into middle distance, not really at Jareth, she goes through the motions necessary to achieve the Climax…
…And then she stalls on "kingdom as great." While she’s wracking her brains, Jareth takes the opportunity to butt in with a truly ridiculous show of groveling: the "Do as I say, and I will be your slave" speech that has launched a thousand kinky OTPs.
Sarah continues to try to remember the next Step in the Formulaic Process, but then you can actually see the moment where she stops. She looks up at Jareth and really perceives him for the first time in that scene. You can see her realizing that, for all his bluster, he’s terrified of her. You can see her deciding that he’s no longer worth it. You can see that weight of terror lifting from her shoulders. You can see her confidence blooming as she looks straight into his eyes, standing up a little taller, even smiling a bit.
At that moment, she’s finally full of herself and her own power. You can see her pride and her hope and her determination when she states with calm finality and some amazement, "You have no power over me." Those words happen to be the Next Words in the Spell of Confrontation, but, more importantly, they are the words with which Sarah seizes her own agency after an entire movie of being a whiny, reactive, powerless girl. HURRAY!!!!