Have you kept a pain journal? Is the pain worse at certain times of the month (cyclic)? Do certain foods make it worse? etc
I also have a chronic pain disorder that started in my late teens and was not diagnosed for a very long time. My cycles were always very painful and very heavy and was told that since other family members had painful, heavy cycles that it was normal. So for 10+ years I thought they were normal, but as I grew older things got worse. At the same time foods started bothering me and we thought it was egg allergy (it wasn't). My dr. kept prescribing antibiotics but finally I realized they weren't working. Then I started keeping a pain diary and found out things were worse around my cycles. The 2nd dr. said it was perimenopause and that problems were normal, and did nothing. Finally the 3rd dr found out I had a large ovarian cyst consisting of endometriosis (misplaced uterine lining). It took 3 drs and 27 yrs for a diagnosis. As for the food problems, I went gluten free (no dr order) and then 2 years later wanted to be checked for celiac. I tested positive in 2 out of 3 areas, but was lacking the antibodies. Last year I wanted a more accurate diagnosis and with dr. permission went back on gluten. That lasted 3 days and started getting sick, so went back on gluten free. The change was immediate.
So have the GI dr test her for celiac disease-its blood work. Also the ob/gyn should check for endometriosis. Unfortunately it can only be found with laparoscopic surgery-unless she has cysts like I did. Mine was seen with an ultrasound.
Has she had ultrasounds of her abdomen/pelvic area?