Karen Brewer is the daughter of Watson Brewer and Lisa Engle. She is a sister to Andrew Brewer, and a step-sister to Charlie Thomas, Sam Thomas, Kristy Thomas, and David Michael Thomas. Emily Michelle Brewer is her adopted sister.
Karen has a goldfish named Crystal Light II, and a rat named Emily Jr.
Her best friends are Hannie Papadakis and Nancy Dawes. She was also close with Amanda Delaney, until the Delaney's moved to another neighborhood.
Karen has an active imagination and believes that Ben Brewer, her great uncle, lives in the attic at her father's house. She also believes that Mrs. Porter, the eccentric neighbor, is a witch.
Karen is the narrator of the Little Sister series.