Here's an observation - most books downloaded for free are never read.
How do you know the torrent led to sales on Smashwords? How much are you selling the book for on Smashwords?
I'm not arguing against torrents as a means of distribution, quite the reverse, but it seems self-defeating to use a giveaway to drive sales of an ebook. Using a free ebook to drive sales of a dead tree edition is well-established now - though it's up for debate whether that will hold true in a few more years when ebook readers are ubiquitous.
If she wants to gauge how widely read she is the easiest way to track that is to ask for feedback emails at the end of the book. Maybe 1 person in fifty will get back to you. Or some other ratio you can pick, depending on how popular you want to feel.