When Kathryn ends up in the last battle of the War of the Last Alliance during a vision, Sauron seems to be the only participant who actually sees her. He tries to grab her before Elendil distracts him, and it looks like he's going to appear in the imaginary forest Smaug brings Kathryn in.
It's revealed in the 16th chapter that this was really Sauron, summoned to the vision in his weakened state. This incident made him aware of Kathryn's existence, so he later tries to possess her to use both her powers and herself in making Smaug compliant to his orders.
In the 13th chapter, Kathryn has a vision in which she witnesses Smaug destroying Dale and conquering Erebor. She then sees the same scenario happening, except this time, Smaug desolates a different city, slaughtering men, elves and dwarves as he fights his way into the keep… to snatch up Kathryn herself. This scenario is even worse than with Dale and Erebor, because Smaug is now sure to kill anyone and destroy any construction he encounters.
"'The Seer… was lost,' Kathryn heard the voice lament inside her head. 'For a dragon will guard his plunder as long as he lives…'"
After the vision ends, Kathryn finds the mummified corpses of the dwarves who were trapped inside Erebor and suffocated to death. Realizing that Smaug would do much worse than this just to get her back, Kathryn feels herself trapped with him more than ever.
"And then, she felt her stomach drop with guilt, terror, horror and dread, as she realised — if her latest vision was anything to go by — Smaug would do much, much, much worse for her sake. If this was him giving his victims a chance, she was terrified to think of what he would do if he really wanted to kill them all."
Heart of Ashes
After her resurrection, Kathryn is trapped in a state of madness, forced to repeatedly suffer from being suffocated by darkness and then burned alive, again and again. This gradually kills her before Smaug saves her.
In the 7th chapter, Smaug kills four dwarf merchants to steal their gold, demonstrating how lethal he still is as a human. He grabs one of them in the face and uses his recently discovered fire powers to emit flames from his palm, practically melting the poor dwarf's face.
While reciting her misandristic teachings to Freyja, Andraya forces the girl to say that should they give birth to baby boys, they'll smother them in their cribs before they can grow up to become the sexual predators Andraya believes all men to be. Makes you wonder if Andraya has actually killed her infant son…
Smaug's human body's gradual transformation back into a dragon reaches a point where it becomes horribly painful. When Kathryn and Faervel find him in a cave, he has become a hideous mix of a man and a dragon, mentally regressed to a wild animal. Since his body is unable to complete the transformation on its on, he's in the danger of dying. When he tries to sprout flame, he hurts his mouth that is too humanlike to protect itself against fire.
In the vision of the 15th chapter, Kathryn sees Ancalagon the Black leading an army of dragons against the forces of the Valar, turning the tide of battle in Morgoth's favor. The behemoth actually flies as quickly and nimbly as the rest of his considerably smaller brethren. His great-great-grandson Smaug is a terrifying One-Man Army, but the devastation wrought by an organized army of dragons is terrible to imagine.
Freyja's death. Discovered by Smaug who has promised her mother to kill them both should he see them ever again, she's snatched up in his jaws, bitten into a pulpy mess and shaken until she dies.
The revelation that it is possible for Morgoth to escape from the void. His demon-son Fankil is actively trying to capture Kathryn and use her visions to find the Door of Night so that he can release his father. Gandalf says that if that were to happen, even Sauron would submit to his former master who will initiate a final battle that would destroy all of Arda.
When Morgoth appears in Kathryn's visions, he's able to see her, just like Sauron in the first story, demanding her to release him with a terrible voice.
