You did not mention whether the gallstones were causing any symptoms or they removed the gall bladder simply because it contained stones. The current thinking is that the gallbladder should only be removed if the are any symptoms from the gallstones. After the operation, most people actually put on weight because their symptoms are relieved and their appetite improves and they eat more. In your wife case the reverse has happened. It would seem that the symptoms for which the gall bladder was removed are still there or are even worse. You mentioned that she has acidity and loss of appetite. She may have peptic ulcer disease which would need investigation and treatment.
I would suggest that you should consult the doctors who treated her gall bladder problem. Her loss of weight is a serious problem and you may have to consult a physician who can investigate it further.