I assume ur wife has seen a gastroenterologist, if he has performed all the usual tests (colonoscopy, endoscopy, food allergy tests etc.) and the results have come back negative, i would assume she suffers from IBS. IBS is a diagnosis of exclusion given to functional GI tract disorders. I would suggest not eating big meals at one sitting but instead, eating 3-4 small meals throughout the day this should reduce the bloating. In my experience i found that having a glass of lemon juice first thing in the morning also helped with the bloating.
I have also found great benefit from using Librax (which is an ibs medication) this should be prescribed from your doctor.