Recently on a visit to our friend's place, my daughter witnessed my friend's 9-year-old son smack/punch a male adult. (They were playing rough and the adult pushed a little too hard and the boy fell down. He was a little hurt and probably also embarrassed. When the male adult when over to see if he was okay, the boy wheeled around and smacked/punched the adult.) The adult was really angry and proceeded to yell at the boy. Eventually the mother came in and verbally disciplined the child and told him why that was the wrong thing to do.
Recently, on a few occasions, my daughter smacked my wife. We think that it was because she witnessed that event.
Immediately after the behavior, we gave her a timeout and explained to her that hitting is not good. We also reminded her that what she saw (boy hitting adult) was not right and not acceptable.
How should I handle this going forward?