It could be a bug or it could just be Kristy's ability. Since with the initial deck, it will be impossible for you to beat. I recommend buying cards, there are some cards that allow you to cause a lot of damage and that way you can easily beat Kristy.
i can't tell if the steal 5 height ultimate card works, i say this cuz i use it then nothing, i kept a close eye on my height and the enemy and theres no + or - 5 height, its like it got sent into the void. sure demo's have bugs and need working on if the creator of said game has only them, idk how many people you have working on this with you nick but the game is fun despite the small bugs I've ran into, the game's 15/10 even with kristy being immortal