Let me try not to disappoint you too much: SheepShaver will perhaps run Office and the other programs your mother-in-law needs, but not as stable as in her previous 10.4.X installation. Also, if printing or stable networking is required from the OS 9 programs, SheepShaver should not be your first choice.
I wouldn't yeopardise that perfect classic install by trying to get it to run with SheepShaver. SheepShaver requires a separate hard disk image to run from, something classic doesn't provide.
If you're still determined to try, then get a decent rom file from somewhere like www.redundantrobot.com
and install mac os 9.0.4 from a universal install disk and copy (not move) the programs you need to a shared folder with SheepShaver and then to the hard disk image.
If you proceeded to that point and have additional questions, please ask them here.