Kytana knew it was a fools errand. Knew that if she drew off anymore of her reserves that it could kill her, but she couldn't stand by and let him end the climb he had made. Let him kill Luke, or keep up the attempt. Even though she knew Luke was not weak, Kylo had to be stopped. She knew that fit of rage. Knew the mission, she had lived it four thousand years before the young man was drempt up.
She forced herself to stand. She abandoned one of her sabers, and instead called to her hand a blaster she knew had been hidden in the old Mandalorian's work bench. She wouldn't have to depend on her strength to use it. Even if she would have to depend on not making a deadly shot. She took aim at her Padawan. And fired. Hoping the need to swing his saber to avoid being hit by the blaster's bolt, would distract his focus enough that Luke would see reason.
"Kylo. It is not your mission to kill this man off. It is his. Are you so weak that you still do his bidding though you are far from his reach? Do you need the approval of a being that is far older than... Force knows how old he is! He is weak! He must prey on you to have any hold on the Galaxy! You are stronger than him, and his goals! You can break his hold on you, just as I did. Just as Malak did! Be your own man and stop this!" Kytana had to hope she could reach him. She was not talking of Luke, of course, but the thing that was the Emperor. "Are you going to let a kriffing moof-milker decide your life for you?"