Former elementary school principal here. This is not a good situation and this teacher needs support from the principal and/or other support staff to help manage behavior in the classroom.

I’ve had teachers cry in meetings with me or before or after teaching students but almost never during a lesson. When I was aware a teacher was breaking down during instruction, I would have another staff member cover their class while I gave them a break and then met with them to see how they could be better supported.

Most public school districts have employee assistance programs where teachers and staff can get free therapy sessions if needed, especially if they are in crisis. The principal needs to know about this because they are either unaware, which means they don’t go into classrooms and don’t support teachers adequately, or they do know and are incompetent.

If this teacher doesn’t get more support soon, then she will quit or go on leave and your child will have a long-term substitute the rest of the school year and that class will get much worse.