IDK, I kind of disagree. Reporting it and getting a small child counseling may make more out of it than what actually happened. If there is any concern regarding possible physical injury, I would see the pediatrician. Maybe take this opportunity to have a nice low key discussion with your 3 year old about good and bad touching while playing with friends. Just to make sure she gets the idea that, if this other child did do something, that she shouldn't repeat it with her or anyone else. Then I would take a wait and see approach, we are talking about 3 and 6 year olds here, right?. By all means either avoid having them play together or restrict play to supervised areas only. I know avoiding can be difficult if they are family or neighbors. Now the other parent seems like she and her daughter may benefit from the counseling. Sounds like she it handling the behavior directly though, maybe just offer positive support to her.

I just wanted to add that I know it is easy for me to see this situation calmly because I am sitting in a 3rd party position. With my own childhood abuse issues floating in the back of my head, I would find this situation difficult to deal with calmly if I were living it. It would likely take me some time to separate the other child's behavior from the child.

Good luck, I'm sure you will make the decision that is best for your daughter.