Which versions of MacOS and Microsoft Word were running on your wife's Mac? Are all of the Word files affected, or is the problem associated only with old Word for Mac files?
Microsoft Word for Mac has been through many revisions since the 1980s. The default document format for Word for Mac changed several times over the decades. The older formats were very different from one another and they are also different from today's ".docx" format.
Note: Before the UNIX-based MacOS X 1.0 appeared, there was the Classic Mac OS, which did not need or use file extensions. Word files from that era may or may not have ".doc" extensions in their filenames, but that doesn't matter. You can easily rename a file and add a ".doc" extension if it helps.
As Word for Mac evolved over the years, Microsoft incorporated converters that could read the older, obsolete Word file formats. It was automatic and transparent. Word for Mac 2004 was the last version that could read and convert the oldest format of Word for Mac files. If your wife's files are that old, then Word for Mac 2008 and later cannot read them. I have Word for Mac document files from the 1980s and 1990s that cannot be read by any current version of Microsoft Word. Any version of Word can find the "text" within a document, but if you do that, all formatting is lost and there is a lot of garbage to sift through.
My Not Helpful Solution:
I have a very old Mac running Mac OS X 10.6 "Snow Leopard" with Word 2004 installed. It is a VMware Fusion "virtual machine" that can run in its own window on a modern Mac. Unfortunately, that solution will not work for most people.
Without more specifics about the problem and the files in question, it is difficult to suggest other ways to solve the problem.
I like the idea of trying LibreOffice. Choose LibreOffice over OpenOffice. LibreOffice is essentially the same as OpenOffice. They split about ten years ago, but LibreOffice has been much better maintained and supported since then. I use and like LibreOffice on other systems, but never tried it on that ancient Word for Mac file format.
Hank Lee suggested converters, which may work if your problem is not that ancient Word for Mac file format. Few converters can read the ancient format, and to the best of my knowledge, they are all commercial products.
Hank Lee also suggested MacUpdate. AVOID MACUPDATE!! They cannot be trusted. MacUpdate may try to install adware or other unwanted software in addition to whatever application you download.
If you find a product you like, download it from the original developers' websites ONLY. No exceptions and no excuses. Take the time and make the effort to figure out the original developer and find their website.
Please post more details about the versions of MacOS, Microsoft Word, and the document files that have issues. Please tell us whether the problem is with all documents or only certain ones. What is different about the ones that fail?