IBS is a common problem of people less than 40 yrs of age. It may be a diarhhea predominant or constipation predominant but may have both in a less often cyclical manner. Pancreatic exocrine insufficiency may be a cause of loose stools too, which would have a fatty characteristic and may have accompanied abdominal pain. It can be ruled out by a Stool fat estimation test and would respond to treatment with pancreatic enzymes like pankreoflat along with food. But IBS wont be relieved after that. So you first need to confirm the diagnosis, whether its IBS or not. IBS patients present with abdominal pain or discomfort relieved after passing stool and associated with change in frequency and consistency of stool and often an urgency. It is often associated with anxiety, insomnia and nervousness. It seems your wife has IBS. I suggest 3-4 litres of water per day, fibrous foods like fruits, green leafy vegetables, bran, oat. Lactifiber at bedtime will be good for hard stool or you can use plain isabgol. Amytriptyline 25mg at bed time may also help.