Bonnie Seabury (b. 1998) is the daughter of Jane and Kenneth Seabury, the younger sister of Brian Seabury, and a resident of Old Larkin in Larkin Mills. She became friends with Alexandra Quick when she and her mother moved from Chicago to Sweetmaple Avenue in Old Larkin, and looked up to the older girl.
During the summer of 2006, she and her brother accompanied Alex to Old Larkin Pond, where Alex believed a naiad lived, but left Alex at the Pond to get home before dark. Two days later, Alex visited the Seabury's and convinced them to return to Old Larkin Pond and help her search for her bracelet, which she had dropped there. Bonnie and her brother snuck out and met Alex at a nearby park, witnessing her altercation with Billy Boggleston and his friends. They made their way to the Pond, where Bonnie spotted the bracelet at the edge of the Pond before a kappa tried to pull her into the water. Brian and Alex incapacitated the kappa, pulled Bonnie to safety, and retrieved Alex's bracelet, but the Seabury's furiously returned home without speaking to Alex.
Bonnie saw Alex again on Christmas Eve of 2007 while ice-skating at Larkin Mills Pond. She seemed happy to see Alex, but was dragged away by Brian after Brian and Billy mocked Alex by calling her a freak.
In August 2008, Bonnie ran across Alex again at the Larkin Mills Mall when Alex caught Bonnie shoplifting scrunchies at a store. Alex made Bonnie return the items before Brian and Boggleston arrived.
On Christmas Eve of 2008, Bonnie and her family visited Alex's family upon their return to their reconstructed house at 207 Sweetmaple Avenue. Bonnie and Brian saw Charlie and Nigel for the first time, and Bonnie asked Alex if she was really a witch; Alex, remembering what she saw when she faced the wild boggart at Charmbridge, claimed that magic and witches were imaginary, and insisted that Bonnie forget all of the fantastical things she thought she'd seen.
Through the first half of 2009, Bonnie continued to get into trouble, which Mrs. Seabury blamed on Alex having been a bad influence on the girl. In July 2009, Bonnie followed Alex to Old Larkin Pond, where she witnessed a conversation between Quick and Diana Grimm and realized that Alex was, in fact, a witch. Alex attempted to scare Bonnie off by acting callous, but Bonnie was not put off, and the two walked back to Sweetmaple Avenue together.