Buddy, you can legally sell Kaplan materials if you paid for them (which I am sure she has since you can't find Kaplan books on the street for free). You will find legal auctions of Kaplan stuff on Ebay all the time, and EBay enforces copyright laws in its auctions quite zealously. You can sell books, software, whatever. Otherwise places like EB games or CD exchange etc. would be shut down.
The only problem with buying used copies of Top Score Pro is that they are time activated - they only function during certain dates. Such as between Jan 03 - Aug 03 or whatever (I don't know the actual dates - the CD comes with the active dates). If anyone needs more info on the time enforcement of this product PM me.