What to do in the face of a wrongful termination claim?

Q. We just let an employee go after less than a year of employment, due to her attitude toward her co-workers. Before we could even get into the why (bullying), she abruptly left. She is now threatening to sue us for “wrongful termination” unless we hire her back, and she also stated she "wanted to get the office manager fired.” I would appreciate any suggestions on how we should handle this situation. – Laura, Illinois