Kids' Stuff by Sue Vyner & Robin Lawrie

This title is part of the Go For It  series of dramas based on family, school, and relationship problems. It wasn't that Zoe still believed in Zara—imaginary friends were kids' stuff after all. But Zoe's family doesn't understand her, and Frankie James is everything Zoe isn't—popular, gorgeous, sophisticated. When Frankie finds out about Zara, Zoe knows she's heading for trouble.