I was working as an 11-7 supervisor at a nursing home when one of the CNA's came to me and told me that one of the other CNA's had "popped" a resident on the hip for fighting her when she was cleaning him.
There was no harm to the resident, not even a reddening of the area, but that wasn't the point. I had to send her home and fill out a report, and of course she was fired. When I talked to her, she pleaded with me not to send her home, citing the fact that she had children and needed the job, that the resident wasn't hurt, etc. This was someone I had often gone to give a ride to work in my own car, one that I liked and enjoyed her company. It broke my heart, but there has to be zero tolerance for this kind of thing.
You made the right call. Tolerating little things leads to bigger things. If it's "no big deal," then it becomes standard, which sets the stage for the next level. In a way, you're doing that nurse a favor, giving her a wakeup call so that she can examine her behavior before she becomes something even uglier.