Final answer:
The correct word for the given sentence is 'sloughing,' as it implies shedding superficial layers, leading to a genuine writing style.
Step-by-step explanation:
The correct word to fill in the blank is 'sloughing'. This means to shed or remove layers in a metaphorical sense. The novelist was shedding the artificiality of her first book, which implies getting rid of something superficial or unneeded. On the other hand, 'portending' is not the correct word as it means to signal or indicate something typically bad, about to happen, which does not fit the context of the sentence. Therefore, the correct answer is option (b) Sloughing.