This is a teacher, not just some volunteer who doesn't know any better.

She has been educated and certified to do her job because by doing her job poorly it makes a significant impact on the long term outcomes on a child's life.

In other words she should absolutely have known better as a fundamental part of her job or she just couldn't be bothered to include the child in the event and if she is either that unqualified or that callous then she should be fired.

I spent a decade working in education with kids from preschool to high school. There are very clear fundamental principles around these types of situations.

This is actually so egregious that it is something that you would see in a training video and people would scoff because it would be so clearly out of line that it would be assumed no one would ever actually do it.

This is literally a text book example of what not to do.

Also, if she thinks that this is ok to do in an event with the community watching, what sorts of things does she do when she thinks no one is paying attention.