From your history I feel there could be gastric erosion ( ulceration) in her stomach as there is pain on eating.THis is a rare possibility in 5 year old. Mesenteric lymphadenitis is a possibility.Definitive diagnosis is made by identifying the underlying cause of the gastric mucosal inflammation and/or by tissue (gastric) biopsy. For example, the major infective cause of gastritis is Helicobacter pylori (H. pylori). This bacterium can be detected by breath, blood, stool, immunological and biopsy tests.Biopsy of the stomach mucosa, done during endoscopy examinations, is often used in patients to identify the causes of chronic gastritis and may allow visualization of mucosal erosions and other stomach mucosal changes. Abdominal X-rays or barium studies (upper or lower) may demonstrate the presence of thickened mucosa and folds that are signs of inflammation in the stomach. Your doctor can help determine which tests should be done, including ancillary tests that may help identify other causes of the non-specific symptoms commonly found with gastritis. I would give Rantac syrup and watch.For nausea and vomiting another medicine like ondansetron could be give. In your case diagnosis by endoscopy and ultrasound and Xray would help. You can discuss with your doctor. Regards