Do I have to follow school crossing supervisor directions when crossing?

I just crossed the road on a zebra crossing, there were no cars coming and I got stopped by the school crossing supervisor and she was pissed that I didn't wait for her to stop the traffic and she told me she's in charge of the crossing and I have to wait for her. I am a foreigner and I don't have idea about these kind of rules. Was she right or was she just being a Keren? FYI there were no kids waiting to cross