This could be due to gastritis
which can be caused due to indigestion
or some intolerance regarding the food item.you can do one thing you can avoid giving her all sorts of external food items especially which contain water.Prepare food for her in house and give her fresh.
Also you can give her medicine Ars Alb 30 one dose of homeopathic
medicine before taking meals for a week which will work for her and help her to prevent vomiting
and proper digestion of food