She can only sue outside worker's comp for damages if there was a Third Party, other than another school employee, who was negligent.  For example, if the school contracted out with an outside company to provide school lunches, and someone with this indepedent contractor spilled something and neglected to clean it up or warn of the danger, your wife might have a claim against such an outside contractor.  Absent such a situation, she is going to be limited to worker's compensation.