Do you feel confident enought to talk to "Miss Susan" yourself? I know it can be hard to muster up the courage but it doesn't sound like the owner is going to do much about it (if she seemed shocked it but be out of what she thinks is this persons character). I imagine she would have difficulty bringing it up to the teacher and most likely would not make enough of an impression to effect a change. I can almost envision a discussion in which they think you are an over-reacting mother and comisserate about how hard it can be to handle a group of small children...
Let me share with you how I handled a similar incident:
I once had an incident when I picked my daughter up at preschool and her class had a substitute teacher. The teacher had a child by the wrist kind of dangeling him (feet were not touching the floor) over the spot on the carpet that he was not cooperating about sitting on. I was horrified! I immediately stormed over to her yelling "Put him down!" as I came. She mistook me for the mother and began telling me how awful he'd been behaving all day. I immediately corrected her presumption, gathered my daughter and continued to give her a piece of my mind.
I immediately went to the owner and explained what I had seen. Her comment to me was "some children are easier to handle than others, sounds to me like he wouldn't sit in his spot." (Totally defending the teacher!) I KNEW by that remark that nothing was going to be done, so I called CPS and made a report from my cell phone right there, then stood outside and told every parent coming to pick up at that class what I had seen. Needless to say only 4 of the 13 children were back the next day.
Apparently the sudden drop in enrollment was enough to get the owners attention and she called us all to explain that she would never have that woman substitute again in her school and that our regular teacher would be back the next day and could we please put this "unfortuate incident" behind us.
I never did return (mostly because her first response was to defend the teacher).
Anyway, the point of my long story is that sometimes the person who is directly impacted by the event can make more of an impression. I would go to Miss Susan and explain what my daughter had said happened with her and scare her by saying that you felt obligated to make a report of it and hope you don't ever hear that she is being physically punative with any children again.