What could cause nausea after eating every time she eats for days at a time but then it will subside for days at a time as well?

Anxiety: is state of tension, apprehension, worry, uneasiness or fear. It may be related to anticipated danger or arise for no apparent reason. While mild episodes of anxiety are common and do not usually require treatment, more severe forms can be chronic and debilitating. Symptoms of severe anxiety: insomnia, chest pain, nausea, palpitations, tremors, and parasthesia.