"SHe looked and smelled like a peppermint drop"

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This is a reference to Scout's teacher Miss Caroline. She is new to Maycomb and brings with her a new way of teaching. She is  a naive character that is blinkered in the way that she only knows one way of teaching which Scout disagrees with.  MissCaroline often has trouble disciplining the children and does not understand  the family economics of Maycomb. 
The way in which this statement is written by Harper Lee points towards the idea that this is the older more cynical side of Scout's personality. She says it in an almost patronising way, as though she is mocking her naivety.