Out of sheer curiosity, how do you know it's there?
That would seem to me as the kind of thing that wouldn't be noticeable unless:
A) The person tracking your stuff was making it blatantly obvious, or
B) An antivirus program told you it was there
In the case of A, threaten to report them to the authorities. Everything she gets into with your username / password (not to mention putting the keylogger there in the first place) is a separate federal felony offense.
In the case of B, use said antivirus program to remove it.