Did she compress the folder she has been saving and opening her class files inside? If so, when you open a compressed folder the OS actually places the file into a temporary folder when it removes it from the folder upon an open operation. This is because when a compressed file is taken out of the compressed folder it has to be uncompressed. In order to un-compress the file it has to be placed into a temporary folder.
So, when you save a file again, it is actually saved into the temporary folder, not the original compressed folder.
This causes individuals to often "lose" their files. When an individual is unaware that the file is actually being saved into a temporary folder, not in the original folder inside their Documents folder, they can often lose the edited file. This is because the "old" not edited copy is still inside the compressed folder, but the edited copy is inside the temporary un-compressed folder, which is *not* in the Documents folder.
In order to *find* the lost file, you need to perform a search with the search option on the Start Menu. Open Start, click on Search, click on All Files and Folders, then on the next page enter either the file name, or some phase within the file, and select the drive you want to search, usually the C drive, but if you use a different drive, select the one which holds your system files and profile data.
She could also go into her profile folder, into Appdata, or application data, then into Local Files, and then just click on every Temp file you can locate and search manually for this file.
The profile folder in XP is under Documents and Settings, Your User Name, then Application Data, then usually Microsoft, and then Temp or temp, etc.
The search feature usually does an excellent job though and is a whole lot easier.
If this was not a compressed folder then it is possible when she went to save the document she wasn't aware that she saved it into the wrong folder.
Anyway, just a heads up on compressed folder use, when you want to open a file, just drag it out of the folder and drop it onto the desktop, and open it from there, or create a folder for this purpose on the desktop, or in the Documents folder, as long as the Documents folder has not itself been compressed.
Hope this helps, good luck and I hope your friend finds her file. Please have a nice weekend.
*edit* It is also possible the file has become corrupt. Try to open the file from within Word. While in the Open dialog box, click on the small drop down arrow next to Open, and click on Open and Repair. That might do the trick.
If that doesn't work, you can check and see if the file extension has somehow been disrupted. Does the file have the Word icon? Does is have .doc at the end of the file name or a generic extension?
If so, right click the file, (once you locate it that is) and select Rename. Change the extension from whatever it is to .doc, and answer Yes to the warning, and it should then open in Word.
If you do not have file extensions showing, go into Folder Options on the Tools menu, in Windows Explorer, not Word, click on the View tab, scroll down to the option to Show File Extensions, and put a check mark in front of it, click OK, and now file extensions will show up at the end of file names. This is a good idea to set this option anyway so malware can't slide past you by attempting to hide behind a "safe" extension, like this: wordfile.doc.exe. the .exe is the real extension but all you would see is the .doc and think it is a document when it is really an executable which will execute when double clicked and harm the system.
Once file extensions are shown, you can check what file extension is on this file, again, once it is located, and make sure it has .doc. You can also right click and choose the application to open it in. If for some reason Word is damaged, you can change the extension to .txt and open it in Notepad, and print from there too. It has saved my behind a number of occasions.