Well, you still haven't said what method you are using to scan, but for example, when scanning using Epson Scan with my Epson Perfection 2480, there is a drop-down adjacent to the scan button which allows me to set such things as the location for the saved document, the naming method and the image format. The Image Format drop-down offers: JPEG, Bitmap, multi-tiff, tiff, and PDF.
Alternatively, assuming your friend is using Windows XP, she could simply save the attached jpeg to her desktop, right-click and choose "open with", then "choose program", highlight the entry "Windows Picture and Fax Viewer", check the box "Always use the selected program..." and click OK.
She only needs to do that once, and subsequently, the jpegs should open automatically with the correct application.