My Granddaughter Has Persistently Been Sick. Terrible Cough, Diagnosed With

My granddaughter has persistently been sick. Terrible cough, diagnosed with RSV. Never rebounded. off and on low grade fever, joint pain. diarrhea, upset stomach, no appetite, very emotional. She seems to be small for her age. They haven't found anything wrong. Calling it a virus and want her to fight on her own. when she cries and giving her small meals kind of help.