She was played by Aliyah O'Brien.
Two years prior to the film's events, Kim Balmain was involved in an illicit affair with Michael, the husband of Jennifer Shannon's longtime friend, Sandra. When she learned about Michael's priceless baseball card collection, Kim tracked Michael to a barn that contained the collection (among other priceless items) and killed him with a single gunshot. Kim's plan also included framing Sandra for the murder, and after killing Michael, she also killed her rich husband, Robert Balmain.
The beginning of Kim's villainous reveal came when she was shown texting the proprietor of a pawn shop, telling him that she would not be attending. Kim completely revealed herself as the villainess when she appeared at Sandra's home with a gun pointed at her, telling her to call Jennifer and tell her to come over. Once Jennifer does, Kim ordered them to head the barn, all the while revealing that she killed Michael and had an affair with him. Kim planned to kill Jennifer and Sandra by setting fire to the barn, which she does, while she gets away with the collection. Jennifer and Sandra escape, and later on, Kim is arrested while in her car trying to escape.