I thought I had IBS because I was way too young to have colon cancer. Turned out I was wrong. I trust your friend has gotten a firm diagnosis following a colonoscopy.
Now, missing a large part of my colon (having a semicolon, as it were), I have similar dietary and bowel troubles. The best I can say is that experience is a good teacher. Trying the things the folks here relate is probably a good idea. Some may work and some may not, but experience is the best teacher.