I agree it was unprofessional from the police officer. Pravpi's and Admerius's perspectives are the most rational one I've seen. If this had happened in the US for example the woman would've sued and probably won millions in a lawsuit. I don't know anything about romanian law, so I can't compare.
The woman was a teacher accused of physically abusing her students. Given the way she reacted to the cop, it's just further proof she's obviously guilty. She had no problem slapping not only an adult man, but a cop. Do you really think she had any scrupples about doing it to children much physically weaker than her? The cop reacting the way he did puts the whole case in jeopardy. I can understand the reflex, but I can't approve of it, given the position of authority he is in.