Note that according to the Sun, a lot of the 2000 just wanted to see her speak. A lot of the 200 were in the hall to heckle her.

She said that they were DEMANDING that the books be burned. Then she lied, pretending that there actually had been a book burning.

In general, I think that speech laws should restrict lying more than it does. But if it not specific slander, she is allowed to lie.