When the undead outbreak occurred, Karen, her mother Helen, and her father Harry were attacked by a horde of zombies which turned over their car and bit Karen. With Karen too ill to move, they joined with Tom and Judy and hid in the cellar of a Pennsylvanian farmhouse.
Eventually, Karen dies of her zombie bite, reanimates and devours her dead father's flesh. When Helen comes down into the cellar, Karen advances on her mother and guts her to death with a trowel. Karen then goes upstairs and attacks Ben, who throws her off and locks himself downstairs.
Karen and the zombies at first try to break into the cellar, but they eventually give up and abandon the farmhouse.