Unusal rash

My daughter, who is 18 years old, has a funny looking bumpy itchy rash over her arms and trunk. At first it started on her arms and then spread to her trunk, bach and up her neck going toward the face. Initally she did not have a fever. But had one night of a fever. She was prescribe a steroid and the rash look like it was going away. She completed the 5 day medication and developed soreness of the neck shoulders and back. 3 days later the bumpy rash has returned. She has been left feeling tired. What could this be? At first it looked liked measels? There was a recent outbreak of whooping cough at her school. Could this be a reaction to that?