Madness is in the eye of the beholder.
Antoinette Cosway is a young girl who grows up in Jamaica. Her history is one of plantations and violence and a sensitive nature forced to endure.
When she is married to Rochester, she is thrust into a world which is not her own and her lack of acceptance of it is soon attributed to madness. From then on, Antoinette is a burden; trouble which needs to be hidden away.
We know there is instability in her family but her new husband is given this information in vengeance and willingly uses it to alienate himself from her.
It is only her renaming which I find unconvincing. Rochester calls her Bertha because he likes it. I suppose this can be seen as an example of the way he appropriates her but to me it seems unnecessary.
From lush, green Caribbean vegetation to dark, foreboding Thornfield Hall, Antoinette is transported. An attic becomes her home and a drunken servant her guard.Fire destroyed the Coulibri estate where Antoinette was raised and will play an important part in her future, as anyone who has read Jane Eyre knows.