I have no idea why your GF continues to be your GF.
She is clearly smarter than you...
(Maybe she doesn't really care about the torrents, and just wants to stalk you (!) )
If you really want your "privacy", then create a new user account, just for torrents. Give it a nice, strong password.
Don't give your password to your GF!
Lastly - if you have to use the same computer as the rest of your household, then you probably have to put up with loss of privacy.
Get your own computer, encrypt the hard drive, give it a good password that only _you_ know.
and solved (well - except for your other personal issues - a.n.d. the NSA )
She's your GF, maybe she's just trying to help you with your habits?
But, look in your Caches folders, or in Application Support folders, or look for the name of your torrent app in Preferences folders.
You can also search for files that are newly created, or modified, when you download a torrent. There's only about 10 or so different locations that I can think of, and that depends on which torrent apps you use, the torrent download settings, and what version of OS X you have.
Or, you could try a different "hobby" that's not so offensive to your GF (I suspect she keeps track of you because she likes you - think about that for a while )