Despite the conspiracy theories that abound, here is my guess as to what happened:
Writing chick lit is HARD. Writing any book is hard -- and time-consuming. From Danielle Steel novels to A Heartbreaking Work of Staggering Genius, it is difficult to find a plot arc that works, mix in some somewhat believable/sympathetic characters, write the whole damn thing, and have the Book Fairy deem your drivel good/marketable enough to sit on store shelves.
So, after getting her book deal, too tired and busy to deal with all of her obligations, Kaavya Viswanathan did what any student would do on the eve(s) of her book's deadline(s): She sat down at her computer, maybe with a cup of really strong coffee, took her fave McCafferty novel (which was the style she was going for anyway) and, out of desperation, started plucking out little scenes and turns of phrase, changing them slightly, like you would if you were writing a report on Antarctica in fourth grade and using only the World Book Encyclopedia as a source.
When I "internalize" a novel, I internalize scenes and maybe a few choice quotes from my favorite characters. Unless Viswanathan read McCafferty's novels 40 times in high school and quoted them to her best friends and in her diaries, I'm skeptical of her claim. May the drama unfold while the rest of us feel just a little better about ourselves for having written nothing beyond blog entries and checks to our therapists since college.