3 ideas
Once a person is labeled insane, their objections to confinement are recorded as further symptoms. Anger, pleading, and even calm argument all count as evidence for the diagnosis. The patient loses any way to speak that could establish her sanity, so the label confirms itself.
The same distressed woman seems more or less 'mad' depending on how the institution treats her. Isolation, surveillance, and refusal to explain decisions make her agitation worse. Being addressed as a rational adult lets her steady herself. The observed illness is therefore partly produced by the treatment setting, not just brought into it.
A married woman's liberty can be decided through arrangements between her husband and her physician, without her consent. Two men's judgments of her condition become legally and practically binding. Her own account carries no equal weight, so marriage and medicine combine into a single system of custody.