I'm not sure as there is not enough information provided about her role in it.
Since we don't have much details, it's hard to say. But generally, she could play a variety of roles. Maybe she's a protagonist who is trying to uncover the truth behind the story. Or she could be a supporting character, like a friend or a family member of the main character, providing help or creating some obstacles in the process.
There's no official information yet on the role Claire Holt will play in 'Based on a True Story'. However, considering her past roles, she might be cast as a strong - willed character. She could be a journalist investigating the true story, or perhaps a victim of the events that the story is based on. Her character could also be someone who has a hidden agenda and is manipulating the situation for her own gain. Without more information, it's all just speculation.