True, out of context, the reader has to unravel the knots in the 'hers'. I think there are two possibilities: 1. The 'author' refers to the author of the criticism -- The author [Jane] did not see the incongruity inherent in her [Jane's] scathing criticism of writing style so similar to her [Jane's] own.
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Left out is -- her own writing style.
It's not really that uncommon for human beings to criticize others for wrongs they themselves are guilty of.