Her mum, Linda, says the attack happened after a group who had been bullying her suddenly changed their tune and asked her to join them at a festival.
Instead, they took her to a house where is is believed they had planned to rape her.
Despite doing her best to help her girl recover, mum Linda says Cassidy was never the same.
‘Even though I moved her away, she could never go to school again, she couldn’t be around people anymore, a quick trip to the shops often ended in tears or panic attacks,’ she described in a post on Facebook.
‘Cassy was my world, she still is and she always will be. But now I have nothing, and I’m still trying to find a reason to go on without her.'