I first read Jane Eyre
when I was about 7 or 8, I think - the Readers Digest "Best Loved Books" condensed version - and have read it repeatedly since (not to mention Jasper Ffordes' The Eyre Affair
and its sequels), as well as watching several movie versions of the story... And through it all, I'm a bit embarrassed to say that I never thought much about the mad woman in the attic, Rochester's first wife, let alone the way that Jean Rhys did - as the victim both of guilt by association and a strait-laced, conventional, and ultimately vindictive husband who married her without knowing or caring anything about her or the culture in which she was raised.
Antoinette Cosway (later Antoinette Mason, and still later "Bertha", although I have to confess I don't understand why Rochester chose that name for her) is presented as the scion of a family of Creole slaveholders, who as the book opens have lost the bulk of their fortune with England's abolition of slavery. The one-time slaves take revenge on their former masters, in ways petty and great - harrassing Antoinette and her mother on the street, poisoning their one remaining horse, and eventually burning their mansion down around them, killing Antoinette's sickly younger brother in the process. Losing her son drives Antoinette's mother past her mental breaking point, and Antoinette herself is sent to a convent school, while management of her inheritance from her mother's second husband is taken over by her stepbrother.
By the time she is old enough to leave the convent school, her stepbrother has arranged for her to marry an Englishman. Edward Rochester is all too willing to accept her and her sizeable dowry with very few questions - but also is all too credulous when malicious gossip suggests that she is both sexually "loose" and destined to become as mad as her mother.
Sadly, Antoinette *is* driven mad, by a combination of her husband's betrayal and coldness and the potion intended to help her win back her husband's affections, grudgingly given to her by her family's old housekeeper, a practitioner of the folk magic and religion known as Obeah. When she is transported to Rochester's family seat in England to be hidden away in an attic for the rest of her life, she interprets it as nothing more than an illusion, never realizing she has been taken away from her beloved island.