I also have Crohns and would agree with clip clop, its different for everybody, and very much trial and error.
I have problems with oranges, olive oil and sunflower oil, ( including all the spreads with them in aswell ) and coffee.
I have found that I can cope with one or two cups of mild coffe a day, but I only have half a spoonful of coffee at a time.
Its just a case of watching what you eat and what makes you bad, It might be a good idea to keep a food diary for a month or two, if she notes down everything that she eats, and the time of eating, and notes down her bowel movements and pain and the times that she has these, you can then look back and see what is causing her problems, I found this a great help when I was first diagnosed. X