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Moving documents from one form of MS Word to one based on Apple will require some effort, but if you use the Migration Assistant on the Apple computer, it may be fairly systematic enough.
It will be easier for her to convert to Apple, if you have Outlook for Mac on the new computer, I think.
As for whether another sort of email package would be 'better': does she complain about Outlook, as it is? if not, then nothing's better than a no-complaints sort of thing.
A PST file from Windows can be imported into MS Outlook for Mac ... the opposite operation may not be so easy. Everything I've found so far is about the reverse direction of transfer and Import of a PST file.
Note that MBOX files are used in Apple Mail, but PST files in Outlook - so there definitely would be a conversion effort if Outlook for Mac wasn't what is to be used.