A - Incorrect: decided on is used idiomatically to indicate a choice among multiple options, making it incorrect in this context. Also, the pronoun it most likely refers to Peter Rabbit, but grammatically it could also refer to her faith in the book.
B - Incorrect: she herself is redundant and wordy.
C - Incorrect: This answer is excessively wordy.
D - Incorrect: The omission of the word herself from this answer choice changes the meaning of the sentence; it is no longer clear that Potter self-published.
E - Correct: decided to is the correct idiom in this context, and the meaning is clear and concise, and the use of the phrase the work eliminates any possible pronoun ambiguity.
E is the correct answer.