I built one of these, it's really simple and quick to make. http://www.instructables.com/id/Bargain-Price-Book-Scanner-F...

They still warp, but less than laying flat on the table and it's quicker if you do all the even pages, then all the odd pages. Actually the hardest part is making the camera stable so it doesn't move when you press the button.

Lots of info on different hardware setups and scanning software here that can batch translate into pdf and different formats.

http://www.diybookscanner.org/forum/index.php

I remember when I was in my middle school orchestra, occasionally I'd get a piece of sheet music with this problem. If it was bad enough, it might even make it impossible to read the last few notes. If you could fix this for your wife, I'm sure her students will greatly appreciate it!

Ah that; it's a major difficulty. A problem is that not only does the shape warp, but any part of the image that is lifted away from the scanner glass, even slightly, gets blurred quite a bit.