Final answer:
Miss Hinch is not described as an astonishing impersonator; instead, she is portrayed as an unremarkable figure who only becomes memorable due to a singular notable moment.
Step-by-step explanation:
No, Miss Hinch is not considered to be the most astonishing impersonator of her time according to the provided text. The passage highlights that the individual was not particularly remarkable in any sense and had a nature that was 'thin and colorless.' The passage goes on to state that she was easily forgettable until 'one supreme instant, by one immortal gesture,' which perhaps suggests a moment of significant revelation or action but does not insinuate a career of astonishing impersonation.