The third option uses the word snake in a positive and figurative way.
The figurative element present in the sentence is a simile. In a simile, a person is compared to something else usually using the word "like". In the sentence, "like" is used to compare a woman to a snake.
Moreover, the sentence is positive because it states that the woman was like a snake but "fortunately did not enjoy eating live mice". The person is pointing out the positive aspect of snakes' quickness the woman had and the narrator clarifies that a negative aspect of snakes such as eating mice is not a personality trait the woman had.
