I don't have any friends with kids yet, but I know that with my family I just keep my opinions to myself. I don't tell them anything that I think might be controversial which is a lot because we are AP. If they ask me straight out what I would do if I were having a problem they were having I would absolutely be honest, but not judgemental. In your situation I would probably say something like "I would probably sit dd down and tell her why her behavior was inappropriate and what behavior I expected from her. Then she would have a time out."