I don't have any experience with this, but have you started keeping a food journal and checking to see if you can find a correlation to a specific food? Or doing an elimination diet and re-adding foods back in to see if that would help? Does she get enough water?
Considering that you have been dealing with this for 5m, I'd also consider getting a second opinion with a gasto dr if you can.
It must be very hard for both of you.