Two years ago, transgender teenager Brianna Ghey was stabbed to death by two 15-year-olds. The killers had been radicalised on the dark web, while the victim was trapped in an online world of her own. Now her mother has become friends with the parent of one of the murderers. On the second anniversary of Brianna’s death, Esther sits down with Simon Hattenstone to discuss her daughter’s murder and her own extraordinary response.