She was with her wife and guitarist when she was attacked by two women on the street.
The singer-songwriter from Sheffield, who appeared on the show in 2012, shared pictures of the aftermath of the attack on Instagram.
She posted an initial picture holding a clump of her hair. Her face is visibly covered in bruises and cuts.
Another photograph shows the bruises and cuts on her face much more clearly.
She said: "Was attacked tonight after the show in Brighton, along with my guitarist and wife. Sussex Police have been amazing and are pursuing a charge.