My Four Month Old Granddaughter Has RSV - And Was

My four month old granddaughter has RSV - and was taken to the ER last evening. Her lungs were clear but she was coughing and cried each time she coughed.
She has a low grade fever and has been sleeping a lot since last night. She just vomited and hasn't had a wet diaper for several hours. Should we be concerned - how long should is too long without a wet diaper? My daughter is breast feeding and hasn't had any problems with appetite until about an hour ago when she vomited......