Not being sure what state you reside in i can't be sure, but since you were not on duty then it may be illegal for the DON to ask you to write a letter of apology. I mean would they ask a patient to apologize, whether in writting or verbal, for offending another patients family member? I think not. Your hospital should have a clear policy on employee's who are seen as patients and I bet if you dig enough you can find it. As far as the legality issue you could call the state attourny generals office or your state board and ask them. If it is illegal or even inappropriate, then I would calmly begin the process of nailing the DON's hide to the wall, figurativly speaking. If this is her/his response and support of her/his nurses then he/she has no business being a directior or in my humble opinion being allowed to practice nursing.