Issue with lunchroom lady?

I attended my granddaughter's lunch today at school, 1st grade, public school. All during lunch and I don't exaggerate, this woman blew her whistle, yelled to use inside voices, threatened to take away recess if they didn't use inside voices, did take one little boy's recess away, but kept yelling and blowing her whistle. I am disgusted by this behavior and so sad that our kids are being treated this way while in school. These kids were all eating, talking, laughing, trying to relax and enjoy. One little girl sitting opposite me told me she just eats as fast as she can so she can get out of there before she gets in trouble. What should I do about this besides telling my granddaughter's mother? I felt like I was in a prison camp and the gestapo was tormenting everyone while they ate. Should I call the school and complain, call the district office and complain? There was another grandparent there and I wish I would have asked her what she thinks. I'll go again next week and observe and talk to her if she is there. This just broke my heart for these youngsters! Any and all advice/insight is appreciated.