What Is The Treatment For Skin Rash?

My 14 year old daughter has had a rash for 4 days now all over her body, each day something really swells up on her body, her lips ,her hands, her feet, neck and face. She is in real pain and feels bruised and beat up. how can i bring this rash down she is on anti histimines and steriods for allergies but im worried cause it dont seem to b gettin better.