Umm.. not since 1994 or so.
The only problem you may run into is in doc/text files with high ASCII characters. So - if you've got a file with characters like a-acute, e-macron etc (ie: anything coded for by ASCII codes above 0127), then you may have problems since in the dark ages Macs & PCs had different tables between 0128-0255.
So - check to see if she's using any extended characters (say, characters you need to insert using "insert symbol" in MSWord). The good thing is that, if she is, any differences will be consistent, so a simple search'n'replace will sort this out.
The same goes for Excel.
However, newer versions of Office (2000+?) use some unicode format internally and shouldn't have any problems.
but I have no idea when it comes to MSMoney.
Cheers,
Simon