This is a very complex question to consider. It is very difficult to read this text in isolation without any awareness of the later novel, Wide Sargasso Sea, by Jean Rhys, that takes the character of Bertha Mason and places her centre stage. This novel definitely does re-write Bronte's classic and engage the sympathy of the reader for this liminal character. In Jane Eyre, however, Bertha Mason is never given a voice, never really given a personality. She is denied a three dimensional form, and is instead only presented through Jane's impressions of her:
The maniac bellowed: she parted her shaggy locks from her visage and gazed wildly at her visitors. I recognised well that purple face--those bloated features.
It is possible to only view Bertha Mason as Jane and Rochester view her: as an impediment to their happiness, as a madwoman who has lost all reason. However, it is also important to realise the way that if Rochester is a victim, then she is also presented as a victim of madness. Rochester does do everything he can to take care of her, but it is she that has to endure the insanity that dominates her and the gall of having to watch her husband court a new woman while she, his true wife, remains alive, if not well. She is a character that definitely should engage the sympathy of the reader.