I think even if you can't control yourself to be friendly you may need to say it in mild tone for the first or second time. Only if she keeps commiting will you raise the level of your voice or put it in serious tone (black and white) with tones from sincere manner at frist to an increasingly serious tone in subsequent letters. I personally think this is a safer way for ourselves to protect us juz in case if there are any verbal disputes or even disputes in the tribunal if it unluckily happens.