Like many of the above reviewers, I am an older reader (28 - a grad student in English Lit) reviewing this book. Although it has been years since I last read it, I remember it well because there was nothing else like it out there.
Granted, you can find other books with the "Girl against the world" motif (Pennies For the Piper, Jacob Have I Loved, Bridge to Terabithia, Homecoming, Jackaroo, Scott O'Dell's stuff, The Language of Goldfish, Harriet The Spy, the Anastasia Krupnick series, The Secret Window, new stuff by Francesca Lia Block (sp?)etc.), but none of them really speak to a young reader with such a voice of no-b.s. realism as Willo Davis Roberts.
The atmosphere of her books reminds me, as an adult, of Shirley Jackson's and perhaps Ursula K. LeGuin's. If you still love this sort of dark social commentary/one against the world motif as an adult, there are many extraordinary literary writers to check out. Le Guin, Octavia Butler, Lois McMaster Bujold, Shirley Jackson, Tanith Lee (though she is quite a bit darker), Margaret Atwood, Jeanette Winterson, and Angela Carter, among many others.