Elizabeth Brewer, formerly Elizabeth Thomas, is the mother of Kristy and her brothers Charlie, Sam and David Michael Thomas. Following her marriage to Watson Brewer in 6, she became the stepmother to Karen and Andrew Brewer, and in 24, the adoptive mother of Emily Michelle Brewer.

Elizabeth and her first husband Patrick Thomas moved to Stoneybrook when Kristy was an infant. Patrick left the family about five years later. After his leaving, Elizabeth started working full-time and now has what Kristy calls a "terrific job" at a large company in Stamford, Connecticut. Although she claims not to be bothered about Patrick's failure to send more child support money, she has never forgiven him for walking out on the family.

Elizabeth and Watson began dating about four months before the start of the series. They become engaged near the end of book 1 and marry in book 6, which takes place about eight months later at the beginning of the summer.

In 16, Kristy estimates Elizabeth's age at "thirty-seven or something." Her hobbies include tennis and attending estate sales with Watson.