I strongly advise having your daughter evaluated by a paediatrician before starting any medication. Stomach pain and poor appetite after eating even a little food (early satiety) can be caused by several conditions, including acid reflux, gastritis, constipation, infections, or food intolerances. Please avoid giving her over-the-counter pain relievers like ibuprofen, as they can further irritate her stomach. For now, offer her small, frequent, and bland meals, and keep her well-hydrated. A healthcare professional will need to examine her to identify the exact cause and prescribe the safe and appropriate medication.