Jane is happiest during the typhus epidemic. Discipline breaks down and she and her mates get to roam the countryside at will. Without labouring the point, Bronte is clear-eyed about the heartlessness and resilience of children. It's not exactly Lord of the Flies, but it's getting there.
Helen Burns is one of the first of the Victorian martyr children- and one of the most plausible. Think what a horror Dickens would have made of her. Bronte is good at dreamy spiritual people because she was one herself. Dickens wasn't because he wasn't.
The real Mr Brocklehurst sued Bronte for defamation of character- thereby making sure that nobody would ever have any doubt who she had in mind. Twit!