There are several good articles about back pain/posture here. There were a couple specifically addressing the issues us office type folks encounter.
1) Always try to have good posture while sitting at your desk. Keep your feet flat on the floor, back straight, shoulders back.
I have to constantly think about this/work on it because I tend to get lazy and sink back into the chair. If your wife is having pain in the upper back, she's probably hunching over the keyboard or scooting herself closer to the screen. Don't do this.
Is she having vision problems? I find that when it's time for a new contacts prescription, I start doing terrible things with my posture without realizing it because I have to get my face closer to the screen/page to read it.
2) Move around. Every hour at work, get up, stretch a little, look around, move the legs, etc. Gets the blood moving and makes you feel good. Will also wake you up a little bit.
3) There are some specific stretches you can do even while sitting at your desk. I picked up two from articles on this site which I really like.
The first is to do stretches of the upper back. Basically just extend your shoulders and upper spine, Do this a bunch of times. The second is to deload the spine. Put your hands on your chair and lift your ass a couple inches out of your chair. Hang there for a few seconds. Do this like 20 times.