Is Abdominal Pain And Inflamed Large Intestine Sign Of IBS?

I have a friend who has severe abdominal pain. She originally thought it was lactose intolerance, but we aren't sure. After a colonoscopy (which ruled out Crohn's disease and any general colon problems), it was determined that the issue (might) be IBS because her large intestine was inflamed. She describes her pain as feeling like her stomach is twisting-- bad enough that she can't walk. It doesn't cause trips to the bathroom-- just extreme discomfort that comes and goes. She's on meds from the gastro doctor for when it happens, but we're trying to figure out the root of the problem. We don't think it's artificial sweeteners because she's been off those for two weeks and still has the pain. Her blood tested negative for celiac. She had a consultation about the results, and it seems like they don't know what it is. We're at a loss and don't know what foods to eliminate, if any. She has been experiencing this for a little over a year now, and experienced it as a child too (when it was believed to be lactose intolerance). Thanks so much!