I started off teaching first grade in Anderson, an upper middle/middle class burb, got riffed and taught another three years of elementary in an inner city school.
It takes patience to teach first graders in a good school. It takes the patience of Job to teach first graders from poverty. You find yourself fighting a culture war... they don't know "sit down and get quiet," they don't see school as an oppurtunity, they don't know about time outs and indoor voices or that 'fuck you' is an inappropriate response and they don't know how much they can do intellectually... there are no newspapers at home, or books, and no exposure to kids where all of those things are the norm. It's a risk to bring their parents into the school. They get into fights with each other. They get into shouting matches with teachers and administrators. They say things to their child and to other children that won't be found in parenting guides or teacher manuals. You can't assign homework because the books don't come back to school if they go home.
Why do I bring all this up? I suspect that this teacher should have been out of the profession years ago. She sounds like the poster child for career burn out. But I can tell you from experience that it is very easy to explode from the frustration and aim your words at the kids... because they will hear them and they will react... and not at all the things; cultural, economic, political that create the mess and won't be affected by your anger.
I don't know if this is a poverty school. It doesn't look like it from the outside. If it is, I might be willing to cut the lady some slack. Unfortunately her response only adds to the crisis.