It sound like your wife has a condition called Irritable bowel syndrome. Excessive gas is often due to swallowed air.
1. Your wife should avoid aerated drinks like Coke, Pepsi etc.
2. She may be in the habit of swallowing saliva, which results in swallowing of air as well. She should avoid doing that.
3. She should take a tablespoonful of Isabgol husk with a glass of water or milk once or twice a day. This may help push the gas forward.
Finally, remember excessive gas is an innocuous condition and does not indicate any serious illness.