The causes related to nausea,diarrhea,abdominal pain are food poisoinng,gastroenteritis,stomach flu,
lactose intolerance, irritable bowel syndrome etc.Parasitic infestations like amoebiasis
and giardiasis will also cause watery stools, abdominal cramps,nausea,fever etc.She should take a light diet and drink plenty of water. See a Paediatrician.A clinical examination and tests like stool examination will help. Do keep me posted.
Best luck and regards!