Your wife has developed gestational diabetes, which is specific during pregnancy and most often disappears after delivery but she will remain a high risk for diabetes during her life. Although there are few studies which shows good safety of oral medications specially glibenclamide but no large studies available on this issue. Therefore it is best and in interest of both mother and child to use insulin during pregnancy. Go ahead and get her started on diet and insulin. Please note that there needs to be a tighter control of blood glucose levels during pregnancy.