It was in the very end of the film that Laura became a werewolf. As to how she became one, while she wasn't bitten or scratched by either Will Randall or Stewart Swinton, a possibility is that Laura became a werewolf after engaging in sexual intercourse with Will. A line from the movie suggested that those who have a desire to become a wolf will do so, which could be another possibility. Laura began revealing herself as a werewolf when she showed heightened senses in the film's final scenes while describing to her father and to police what happened during her encounter with Will and Stewart. As she walked away, Laura is shown brandshing yellow wolf-like eyes and an evil smile to cement her heel turn.