The iPod holds it's own database of the music that is copied to it using iTunes. If you drag and drop the files directly to the iPod using Explorer you bypass this databasing utility and the iPod cannot "see" the files as it hasn't been told to look for them. Also, The correct folder is a hidden folder so you need to know where to look.
Similarly if you do a listing of the aforementioned folder in Explorer you can see the music files but the filenames are just a string of numbers and letters, the iPod database knows which file corresponds to the correct music track as it is listed on the iPod. There is no workaround.
The functions that control the databasing of the iPod are not a secret and as I find iTunes a bit clunky I use
http://www.redchairsoftware.com/anapod/ and this allows drap/drop functions and has full Explorer integration.
I would just install iTunes on your PC and do it that way or put the tracks on a CD for her to put on the iPod using her PC.