I sing, in a ladies group, at church, the largest group I have sang for was at Crossroads Cathedral in OKC and that was about 8000 people during a musical, etc..I project very well and have been told I could be heard outside when I was trying to talk over the kids in my child care center.
So, that said. The tone of ones voice is often the difference in yelling and talking loudly to be heard. I am assuming she was yelling and that means she was annoyed, frustrated, or angry.
I expected my child care kids to pick up after themselves, they were supposed to pick up during clean up time. Picking up a blanket is a yes, speaking loudly to children who may be starting a fight, yes, yelling at a child to do something that you need them to do, no, that is not appropriate.
I would talk to the director and let her know this staff is having issues that need to be addressed in staffing or further training. It is very stressful to be in a classroom of little kids all day. This teacher may need to go home a bit earlier in the day, they may need to learn how to say things so that kids will listen, they may need to get up and interact with the kiddo's more. The directory will know this person and be able to manage it internally.