Farrer was a young domestic servant and child nurse in Cincinnati. Between 1851 and 1852 four members of the family she worked for died after eating food she had prepared, and arsenic was found.
She was convicted of murder in 1852 and sentenced to death. Her defence was conducted by Rutherford B. Hayes, then a young Cincinnati lawyer and later President of the United States, who argued that she was insane and that her family history, a mother who had died in an asylum, established it. He took the case on appeal to the Supreme Court of Ohio, which ordered a new trial on the ground that the trial court had wrongly excluded evidence of her mental state.
At the retrial she was found insane and was committed rather than executed. She was not hanged.
The case is significant in American legal history for the insanity ruling and for Hayes's involvement, and it is one of the earliest appellate decisions in Ohio on the admissibility of evidence of a defendant's mental condition. The accessible record is nineteenth-century Ohio reports and later legal writing, and the details of the individual deaths are thin.