Gromit
International Man of Misery
How it happens?Danaerys becomes the Night Queen. Everyone dies.
I don't know how this happens, but she wears slightly similar colour clothes to the Night King and when squinting at a poor quality download could be mistaken for him.
Science.
Remember the Night King bending down, picking up a shard and throwing it at her as she flew away on her dragon. She groans as if hit.