Do Managers have rights?

I am in upper managment of a major retail company in Florida. For over a year I have been enduring rumors spread about me and the store manager, which started from other members of management. I have bit my tongue and tried to ignore them to best of my ability. Over a month ago, the store manager transferred, with this, my thinking would be that the rumors would finally subside, yet only a week ago, one of my employees decided to quit because her hours had been cut back(along with all part time associates in the store), in her resignation letter addressed to me she wrote a very vulgur, x-rated statement about myself and the former store manager, then made copies and showed any employee that she came in contact with and then put them in mailboxes and lockers. Along with her were 3 other employees helping compose the letter, they did not help distribute, but they witnessed it and did nothing. I know all of this because I watched it on our store video. Another member of mgt caught wind of it at the end of the night and pulled all the copies he could find, but no one knows if they were all recovered or not. I am being told that because I am a manager, that this is not harassment, that the employee simply stated an opinion. I have been told that I have to come to work and act like nothing has happened, of course with no retaliation, if I retaliate, I could lose my job. All that has been done with the other employees is a statement has been taken from each of them, but from feedback that I have been getting, nothing will be done. Do I not have any rights? Aren't harassment policies put in place to protect all employees, not just non managment. I am a professional, and I can turn the other cheek on many things, but you can only push someone so far, and to be told that you cannot be harassed because you are a manager seems ludacris to me. Is there anything I can do?