She scans it in a scanner, but the music is often in large books that don't lay completely flat, so you still see the warping near the binding.
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.