The first book in s1:e17 is Nancy Drew: The Witch Tree Symbol (#33) by Carolyn Keene. Although I am a red-blooded American girl, I must admit that I have never read a Nancy Drew book. I was a tried-and-true Babysitter's Club chick all the way (come on! Like Gilmore girls, it also took place in Connecticut. I might be a bit obsessed with my state... what of it?!).
Although Lorelai mentions reading all the Nancy Drews, I did the math and that amounts to something like 305 books. And as I'm guessing that most of these books run along the same lines- I'm not going to miss out on reading something important for more "Golly gee, that sure was a tough mystery to solve! Better go get an egg cream!" So I think it's acceptable that I keep it to the "Amish country one" as we know that Lorelai read it twice (so it was clearly the most important one).