Argued, yes but researched, no. If by research you mean that the theme of Bertha, as you put it, is contained and can be extracted from Charlotte's novel. I would suggest that intellectual and moral arguments are difficult if not impossible to separate from the character of the author. Your argument is similar to that presented in Wide Sargasso Sea and, if you would read Jean Rhys's biography, you will have to come to the concussion that Charlotte Bronte and Jean Rhys are moral opposites.
However since this is an ideological argument as opposed to a rational one, the best exposition in my opinion is in the essay
http://www.english-literature.org/es...onte_rhys.html
I hope, 'hopelessdreamer', that you will not fall and choose an original topic, not one that has been beaten to death.