This is an overwhelming number of coincidences, but at the same time, I cannot think that anyone would be so stupid as to plagiarize some of those sentences deliberately. For starters, it would take a great deal of effort to search through another book and find sentences that fit into yours, and secondly, even if you did that, why wouldn't you change at least SOME of the details? I mean, why keep it "170 stores" instead of changing it to "146" or something like that. Unless you were the dumbest plagiarist in the history of the world, that one would be a no brainer.
I think it's obvious that the author read SLOPPY FIRSTS, and I think it's likely that she has a really incredible memory. Given this, I think it's at least POSSIBLE that she didn't realize what she was doing. At the same time, though, I'm tempted to think that when this author got her book deal, she decided she needed to study up on the genre (I think I read something somewhere that originally, she'd proposed another, more literary book, and they talked her into doing chick lit). So maybe she went out and bought two or three exemplary teen chick lit books, and read them a few times to get an idea of how she should write a teen chick lit. And after she read this book (or a few books), some of the sentences stuck with her.
It's scary to think that something like this could be unintentional, but at the same time, if you read really broadly in your genre, the chances of this happening to this degree are slim to none, because you'll have read SO MANY books and internalized SO MANY sentences that you're unlikely to produce a bunch of sentences identical to one author or one book. If Kaavya had read ninety or a hundred chick lit books, even if she had the best memory of the world, I doubt her subconscious would have regenerated so many of Mccafferty's sentences, because she would have had a much larger number of influences. My guess is that this young author studied up on her genre in a very specific way, but didn't have the kind of broad exposure to it that most writers have, and as a result, her "studying" came back to bite her in the butt.