She was a real person, born to a well-heeled farming family, and in her teen years dated a boy from a neighboring farm. His family disapproved of the pairing, so the boy’s mother threatened to curse Rhoda with witchcraft if she pursued her son. The threat was traumatic enough that it precipitated a mental breakdown, and she became convinced that she was being tormented by a spirit named “Old Scratch.”
Rhoda Derry - Victim of demonic witchcraft or mental illness?
NB NOTES Old Scratch is a nickname that often referred to Satan or particular demons. Wiki
She scratched her own eyes until she blinded herself, possibly so that she would never see 'Old Scratch' again