Dear sir, this is unspecific symptom but usually it is caused by IBD, gastritis
including hiatal hernia or food alergies. She needs to do GE work up. It means that gastroscopy and colonoscopy
must be done to rule out any kind of mechanical obstruction. If nothing is found then it can be IBD or some other functional intestinal disorders. If she feels bette rafter vomiting
it means that the air and fluids are "trapped" in stomach and there is a problem with passage of food through pylorus
. It can be caused by hiatus hernia
or pyloric hipertrophy and stomach sphincters disorders. So gastroscopyy with biopsy will rule this out. Also she should change her diet and avoid things which aggravates symptoms.
Wish you good health.