As Fulcrum, she had learned to focus on the situation at hand. Master Yoda had told the younglings that it was imperative to be in the moment, to avoid the lure of the horizon, but it was a life in hiding, a life in the shadows and on the run that had made the lesson stick. Speculating without facts would get you killed. Always, ALWAYS, focus on what you knew.
First, she was alive when she was not meant to be.
She had seen his image when she spoke the words, had resigned herself to the whim of the Force, had fought Vader and known in the moment that she had been just a fraction too slow. Even as she moved to block and try and attack at the same time, she had the moment of clarity where she could see in perfect detail her death in the form of the oncoming swing. The next moment, she was in a void, surrounded by indecipherable whispers and half-forgotten voices.
Second, this was a place where things were changed. With consequences.
She watched as Ezra agonized over Kanan's death, knew that he had pulled her from her time and place and brought her to this shifting maze of could-be's and never-were's and always-are's. If Ezra pulled Kanan from this moment, the former Jedi would live, but the others would die. As they turned away, and the Emperor appeared, and the flames chased them, she knew this was a place that no one should ever be.
Third, the sight of him was enough to make her forget all of it.
A portal surrounded by spirals showed her love holding his blade to Vader's throat. Her breath caught in her throat when he spoke, declaring himself a servant of the Republic, and revealing the man he had been. The flames approached her, and she turned, blasting them back, holding them off as she gazed at the final moments of her love's life, tears falling freely as she watched him face the Emperor. She saw the blow before it came, and turned away, unable to see the moment his life ended.
He was standing in front of her, shining and transparent, his arms raised to the flames. With a gesture, he pushed them back, and with another, the image of the Emperor and his cauldron cracked and disappeared as the portal was broken by the Shatterpoint.
She turned back to the portal, seeing her love sink to his knees, before being blasted across the snow-swept field, landing on his stomach and rolling onto his back. He was mere inches away from her; if she reached out, she could pull him through. Her thoughts raced through her head; he had already held them off so the others could escape, had died a noble but temporally inconsequential death.
But he had died.
As Vader turned away, the third thought proved true, and she pulled him through, his robe sliding off and slowly disappearing beneath the Corellian snow.