Co-worker trying to scam workman's comp?

My co-worker is trying to apply for Workman's Compensation, claiming she injured herself at our place of work, when she did not. It was a preexisting injury, and she continually performs difficult tasks that she could not possibly do if she were in fact injured in the way she claims. Her claim has already been denied once, and now she is insisting all of us (her co-workers) write letters to Workman's compensation substantiating her false claim. How should we tell her no without her making working with her unbearable? (and believe me, she WILL have a fit if we say no)