Rash around mouth and eyes

My daughter, 14, has had a rash for six days now.  It started in the corner of her mouth and the corner of one eye.  When I noticed it, she told me that the inside of her mouth was itching so I assumed it was a food allergy.  I started her on benadryl immediately but the rash spread to both sides of her mouth and both eyes.

I took her to the ER on the second day because she woke up with her face and eyes swelling.  They did not know what it was but gave her steroids and benadryl through an IV and sent us home with a steroid pack and benadryl.  It helped a little but the next day it showed up on the inside of one elbow and on her neck.  

On the third day we saw our general practitioner who believed that it was an allergic reaction to something and referred us to a allergist next week.  She had more swelling of her lips and eyes.
On the fourth day, we went back to the ER because her eyes swelled and she couldn't see well.  They tested her for mononucleosis and strep throat - both negative.  This doctor thought it was probably Fifths disease and told us it would take time to heal.  He said to continue the steroid and benadryl but it wouldn't heal the rash.
Now we are on the sixth day and she has more of a rash on her neck.  What I don't understand is that it hasn't cleared up anywhere.  She currently looks like the joker and a raccoon.  The rash starts in both corners of her math and generates outward to the middle of her jaw.  The rash around her eyes covers the entire eyelid to the eyebrow and underneath the eyes to the cheekbone.
My daughter does have decreased kidney function and has had urological problems since birth.  Recently her creatinine levels have been elevated.
My concern is that the rash is related to her kidneys and if not that, what could be causing the rash?
Any ideas would be appreciated.  Thank you!