Orissa Kane is seventeen years old, the sister of a young man who is building his own flying machine. Orissa provides financial support for brother Stephen Kane and their invalid mother through her office job, while Steve concentrates on his invention. She also supports Steve emotionally, urging him forward. Steve faces commercial and technical competition, and sabotage by a competitor. When Steve suffers a broken leg in a crash and cannot fly, Orissa takes his place. She proves the validity of his craft, and demonstrates her own courage and competence in the process. She wins the top prize in an aerial exhibition and gets a boyfriend too, without ever losing "her humble and unassuming manner" and her other maidenly virtues.
Baum was simultaneously writing a similar story, of a brave girl defending her brother's interests, in his 1911 novel The Daring Twins. The Flying Girl has a strong feminist element in its story: Steve Kane supports his sister's flying, and even suggests that women will make better airplane pilots than men.
Baum's book coincided with the meteoric rise of aviatrix Harriet Quimby, who became famous in 1911 and died in a crash in 1912. The timing involved seems to indicate that Baum wrote his book before Quimby's brief career, so that he could not have been directly influenced by her example.
As part of its promotion of the book, Reilly & Britton placed an advertisement in the 24 June 1911 issue of The Publisher's Weekly. The ad featured a photograph of the garden of Ozcot in Hollywood, with its pergola and summer house. The accompanying text stated that "Mrs. Van Dyne," as a guest of Mrs. Baum, wrote the novel in the Baums' garden. Perhaps this was an admission to the more discerning readers of Baum's authorship of the book.
The book was planned as the opening installment of a series; a sequel, The Flying Girl and Her Chum, was issued in 1912. The series was not a major popular success, however, and did not progress beyond the first two books. The Flying Girl resurfaced in Oz-story Magazine in 1997, with new illustrations by Eric Shanower.