I also have a suggestion. This is something I found out about MYSELF this summer.

Fructose (and excess sucrose--which is 1/2 fructose)
can be an intolerance trigger.

I have a GI congenital defect I was born with, twisted malrotation of the whole GI tract. So I tend to get "used" to upheavals there. What I DIDN't realize is that I have a fructose problem. Now with hindsight, I realize it was always there, but it just seemed to become much worse all of a sudden.

If your daughter has trouble with fruit, esp. apples and pears, if she cannot tolerate apple juice/cider, that would be a big warning sign of this.

I stopped ALL high fructose corn syrup, high fructose fruit, and sucrose and ALL my gas, pain, and diarrhea attacks STOPPED!
I looked this up on the net and found one site that claimed a 1 in 3 incidence for this intolerance.

I have managed fresh oranges, recently. But I don't drink any juices anymore. I take supplemental Vit C daily instead.

I'd suggest an elimination of these sugars for at least two weeks, to see if there is improvement. I discovered my problem during vacation where I became sick and didn't eat ANYTHING for a while besides crackers, water, chicken soup etc. When I had a G2 Gatorade I was sick within 1/2 hour! And that had 1/2 the sugars of a regular Gatorade. Even Jelly on my peanut butter set me off.

Now that I am eating sugar/corn syr free, I feel so much better, you can't imagine! Please consider it if IBS symptoms are resistant to other treatment!