Maybe it is located in the registry of her old machine?
Open up regedit, and Load the Hive(s) for her old computer. (Check the Help Topics if you're unfamiliar with loading hives)
After this, I would navigate to... "HKEY_CURRENT_USER\Software\Autodesk\AutoCAD" and browse around for the CD key.
Please be very careful when messing with the registry... you don't want to turn your own computer into a paperweight!
- rp