Is this it?
http://quiltville.blogspot.com/2005/...ng-primer.html
If so, it's not a book; it's simply directions that you can read online or print out on your printer. As far as I can tell, that website is her blog. I couldn't find a store there.
I found this book of hers on Amazon:
http://www.amazon.com/String-Fling-S...dp/1611690471/
and she has a few other books there too, but none called String Primer.