The assault on Ellie Tunnicliffe, 16, was filmed and put on Facebook, where the terrifying footage was shared thousands of times.
The teen said she felt scared by a group who followed her and "enjoyed" what happened, while she had nobody to help her.
Ellie says she feels "embarrassed" and "terrified" by the incident at Noel-Baker Academy in Alvaston, reports the Derby Telegraph.
But she and her mum have agreed to talk publicly about the attack and its filming to shock other children into thinking twice about bullying.
Ellie's mum Claire O'Donnell says she is "appalled" at what happened. She says she wants people to watch the footage so they would not do the same thing.
And she wants to show teachers at the school "how bad the problem was".