Having read what’s supposedly the full text of the speech (which wasn’t in any of the articles in this thread, sadface) it seems she was planning to talk about how “we only hear about other cultures” and how “being British doesn’t count”.
Which obviously doesn’t justify what happened, but may explain why some teacher was unusually anxious about it all if they were expecting one of the kids to go full Enoch or something.
(Should add that the speech was posted on Tommy Robinson’s Twitter account, so the usual health warnings apply)