I think shackling women was done to prevent masturbation as well…

…as I think they thought this was the cause of many mental illnesses.

1752.   The Quakers in Philadelphia were the first in America to make an organized effort to care for the mentally ill. The newly-opened Pennsylvania Hospital in Philadelphia provided rooms in the basement complete with shackles attached to the walls to house a small number of mentally ill patients. Within a year or two, the press for admissions required additional space, and a ward was opened beside the hospital. Eventually, a new Pennsylvania Hospital for the Insane was opened in a suburb in 1856 and remained open under different names until 1998.

Diseases of the Mind: Highlights of American Psychiatry through 1900 - Early Psychiatric Hospitals and Asylums