I'm not looking at things through the lens of the IBS diet, so my perspective is going to be different than what is shared here. That's why I'm hesitant to say too much about it - I'm not really sure this is the appropriate environment to be discussing a completely different approach which contradicts what Heather says in many respects.
That said, kefir may or may not be a trigger for you. You'll just have to find out. And, you can buy kefir starter from bodyecologydiet.com and use it to make homemade kefir from rice milk (I don't recommend soy for anyone, anytime... see Jordan's book for more info on this).
Most of what I've learned comes from my graduate study of chinese and western medicine, the doctors and health care practitioners I've seen, books, extensive research and over 7 years of personal experience with this stuff. The bacterial dysbiosis is fairly certain when I consider the history and etiology of my condition.