Sulfatrim and ache

My 6 year old daughter was prescribed sulfatrim for a urinary tract and after the seventh day she developed a rash all over her body and her joints began to swell and ache. After a trip to the er and a shot of ephedrine and some other various allergy meds she bagan to get a little better and now after about eighteen hours and the drugs have worn off, she is in full rash and horrible pain. I have called th ER again and they have called in some Dexadron for her. I have given her her first dose of it and she has no change at the moment. After reading some of the horror stories, I am scared to death and not sure where to turn at this point.