...Well, almost. I think Pojansky and Vande Berg do a fair job of explaining how Melissa Joan Hart's character in "Sabrina the Teenage Witch" as well as her two aunts provide girls with a positive role model. Sabrina is obviously different than most of her classmates because she is, obviously, a witch, and is raised by her two aunts. She shatters many gender stereotypes - for example, she loves math and science and is rarely ever passive or submissive. She is smart, independent, confident, and goes through what all adolescent girls go through as they mature into their teenage and young adult years.
Sabrina and her aunts, Hilda and Zelda, use their magical talents/powers (for the most part, with integrity) to achieve their goals. The three make the most out of their unique lives and living situations. Although girls watching "Sabrina" do not have the same magical powers as its characters, they will understand that they, too, can thrive on being different and use their unique differences to their advantage while gaining independence and confidence.
Although "Sabrina" may seem like it was a great "girl-power" program for tweens in the 90s to watch, it isn't perfect. There are very few characters of color that appear on the show, perhaps showing that only white, middle-class girls can be powerful and independent. The authors also point out that although Sabrina does possess these qualities of freedom, she often still gives into gender and relationship norms (such as appearing feminine to please her boyfriend, Harvey).
I think that the authors are taking "Sabrina" a little too seriously. True - if the producers of "Sabrina" sought out to make it a feminist text, then it could be seen as a bit contradictory. However, if Sabrina revolted against every norm and did not maintain some societal (mostly gender-based) standards, she would not have related to as many girls and the show probably would not have been as big of a success as it was.