The whole reason the author claimed it as autobiographical is that she knew it wouldn't have sold otherwise.  Would a reputable publisher have purchased it as a reputable, fact based work of anectodal non-fiction?  Doubtful.  Especially when the author is a white, valley girl who freely admits she gathered her information sitting at a Starbucks. 

Would it sell as fiction?  Again, doubtful.  A white female child fostered to a black family in gang territory?  Running drugs for the Bloods, getting a gun for her 14th birthday, buying a burial plot?  Maybe in a bad Lifetime movie but not the plot details a good fiction agent and/or editor is going to buy into.

So, the savy little liar, sits down and tells her fibs to an established author who uses some of them in her work.  This all of sudden gives her credibility.  If anyone questions her, all she has to do is tell them to go talk the author or show them the book.  Then she sticks a disclaimer in her author's notes that she combined characters, changed names, dates, and places.  That should have been a sure fire sign that something wasn't quite on the up and up.