What did Jane think of Grace Poole?

Before Jane discovers the existence of the deranged Bertha Mason, Jane believes that Grace Poole is the one responsible for all the mysterious happenings at Thornfield Hall.
Grace is a middle-aged seamstress and servant whom Rochester has given special instructions to conceal and care for Bertha. Mrs. Fairfax, the housekeeper at Thornfield, is the first person who attributes the creepy laughter Jane hears coming from the third floor to Grace Poole. This rouses Jane’s suspicion that Grace is a drunken madwoman. Rochester reinforces this suspicion with his untrue remarks, ones he makes to cover his tracks and divert attention from the fact that he imprisons his mentally ill first wife within the walls of his estate.
Jane even tries to catch Grace in a lie after the fire in Rochester’s room. She is offended by Grace’s “absolute impenetrability,” which is how Jane interprets Grace’s lack of a reaction when questioned about the events from the night before. Determined to get Grace to show some sign of guilt, Jane is annoyed when Grace turns the tables on Jane—insinuating that the laughter Jane alleges was perhaps just a dream. This conversation further cements her distrust of Grace Poole.
Brontë uses Grace Poole as a sort of red herring in the novel, a figure that distracts both Jane and the reader from the truth.