Dolly, appears as though she has medium brown hair, with front bangs. When she was first introduced she was wearing a small black tank top. She apparently looks middle school aged. She has a life-support device embedded inside of her body that sticks out from it and has scars on her body. She looks like Misaka Mikoto, implying that she is a clone of hers (albeit a prototype).
Later, after getting all her memories and knowledge passed down to a clone, she no longer has the scars that were present in her previous body. She also has long hair, which she retains after being freed from the facility.

(Source: Wiki)