It sounds a lot like IBS. If there is a reputable integrative doctor near where you are, they can check for lesser known causes. A lot of those guys are total quacks, but I have seen some who provided a lot of help in cases like this where the regular GI doc had nothing to offer.

Has she tried peppermint? Some data on IBS and peppermint extract.

How are her exercise habits? Good exercise can go a long way in helping lots of these issues. Depression/anxiety that needs to be treated?