If someone's entire body is empty of food , is it still possible to throw up? or would they just be nauseous?

Yes - mucus/saliva: If you have an illness,e.g. gastroenteritis, it is still possible to vomit ; more like dry heaves. Usually it results in some saliva and mucus. The nausea will generally improve after vomiting. Start to take in liquids that have sugar + salt + water -- and take several sips every 20-30 minutes. Avoid foods that are high in oils, dairy foods and citrus foods for now.