Wouldn't you use IE or a browser to view jpeg files?
Before she goes and reinstalls, maybe you should check that IE is the default program to view it.
Look under My Computer --> View --> Folder Options ---> File Types then scroll down to JPEG Image
The normal would have Opens With.... and IExplore at the bottom of the window, but I guess that you wouldn't see that if its not working.
And reinstalling is risky, because it may wipe over other files. Unfortunately, there is not repair or System Restore with Win98, hooray for the 90s!