If it were me, I would keep a copy and never let anyone know about it! The hospital will not back you up if something happens to this patient and they get sued. If you have a copy then you at least have something to refer back to regarding the incident. If the patient/family decides to sue the hospital, they can supoena the patient's medical record. The incident report is not part of the medical record, from what I understand, but rather part of the personnel file of the person written up. So I'm not sure that the lawyers could get a copy of it, unless the hospital decides to hand over some personnel files of involved employees to hang them out to dry. Maybe I'm too young to be such a cynic, but I believe it is important to protect yourself.
I'm a recent grad, and I had more than one nursing school
instructor tell us to keep such copies. You can also keep a journal about your patients (at least, those that could end up being problematic). As long as you keep your secret stash a SECRET, you should not have to worry about it being supoenaed.